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AMU MCA Previous Year Questions (PYQs)

AMU MCA 2017 PYQ


AMU MCA PYQ 2017
For any three sets $A, B$ and $C$ the set $(A \cup B \cup C)\cap (A \cap B' \cap C')' \cap C'$ is equal to





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Solution

$ (A \cup B \cup C)\cap (A \cap B' \cap C')' \cap C' $ $ = (A \cup B \cup C)\cap (A' \cup B \cup C)\cap C' $ $ = [(A \cup B \cup C)\cap A'] \cup [(A \cup B \cup C)\cap (B \cup C)] \cap C' $ $ = (B \cup C)\cap C' $ $ = (B \cap C') \cup (C \cap C') $ $ = B \cap C' $

AMU MCA PYQ 2017
Let $P={\theta;\ \sin\theta - \cos\theta = \sqrt{2}\cos\theta}$ and $Q={\theta;\ \sin\theta + \cos\theta = \sqrt{2}\sin\theta}$ be two sets. Then,





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Solution

For $P$ $ \sin\theta - \cos\theta = \sqrt{2}\cos\theta $ $ \Rightarrow \tan\theta - 1 = \sqrt{2} $ $ \Rightarrow \tan\theta = \sqrt{2} + 1 $ For $Q$ $ \sin\theta + \cos\theta = \sqrt{2}\sin\theta $ $ \Rightarrow 1 + \cot\theta = \sqrt{2} $ $ \Rightarrow \cot\theta = \sqrt{2} - 1 $ $ \Rightarrow \tan\theta = \sqrt{2} + 1 $ $ \therefore P = Q $

AMU MCA PYQ 2017
The function $f(x)=x-[x]$ where $[,]$ denotes the greatest integer function is





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Solution

Let $c$ be an integer. For LHL, $ \lim_{x \to c^-} f(x)=\lim_{h\to0^+}[(c-h)-[c-h]] $ Since $[c-h]=c-1$, $ =\lim_{h\to0}(c-h-(c-1)) $ $ =\lim_{h\to0}(1-h)=1 $ For RHL, $ \lim_{x \to c^+} f(x)=\lim_{h\to0^+}[(c+h)-[c+h]] $ Since $[c+h]=c$, $ =\lim_{h\to0}(c+h-c) $ $ =\lim_{h\to0}h=0 $ Thus, $ \text{LHL} \ne \text{RHL} $ $\therefore f(x)$ is discontinuous at all integers. Hence, $f(x)$ is continuous at non-integer points only.

AMU MCA PYQ 2017
If $f(x)=x e^{x(1-x)}$, then $f(x)$ is





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Solution

$ f(x)=x e^{x(1-x)} $ $ f'(x)=e^{x(1-x)}+x e^{x(1-x)}(1-2x) $ $ =e^{x(1-x)}[1+x-2x^2] $ $ e^{x(1-x)}\neq0 $ $ \Rightarrow 1+x-2x^2=0 $ $ \Rightarrow (1-x)(2x+1)=0 $ $ \Rightarrow x=1,\ -\frac{1}{2} $ For $ x\in\left[-\frac{1}{2},1\right],\ f'(x)>0 $ $ \therefore f(x)$ is increasing on $\left[-\frac{1}{2},1\right]$

AMU MCA PYQ 2017
The range of the function $f(x)=\frac{2+x}{2-x},\ x\ne2$ is





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Solution

Let $ y=\frac{2+x}{2-x} $ $ \Rightarrow 2y-xy=2+x $ $ \Rightarrow 2y-2=x+xy $ $ \Rightarrow 2y-2=x(1+y) $ $ \Rightarrow x=\frac{2y-2}{1+y} $ For real $x$, denominator $\neq0$ $ \Rightarrow 1+y\neq0 $ $ \Rightarrow y\neq-1 $ $ \therefore \text{Range}=R-{-1} $

AMU MCA PYQ 2017
If $\sin(\alpha+\beta)=1,\ \sin(\alpha-\beta)=\frac{1}{2},\ \alpha,\beta\in\left[0,\frac{\pi}{2}\right]$ then the value of $\tan(\alpha+2\beta)\tan(2\alpha+\beta)$ is





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Solution

$ \sin(\alpha+\beta)=1 $ $ \Rightarrow \alpha+\beta=\frac{\pi}{2} $ $ \sin(\alpha-\beta)=\frac{1}{2} $ $ \Rightarrow \alpha-\beta=\frac{\pi}{6} $ Solving, $ \alpha=\frac{\pi}{3},\ \beta=\frac{\pi}{6} $ $ \tan(\alpha+2\beta)\tan(2\alpha+\beta) $ $ =\tan\left(\frac{\pi}{3}+\frac{\pi}{3}\right)\tan\left(\frac{2\pi}{3}+\frac{\pi}{6}\right) $ $ =\tan\left(\frac{2\pi}{3}\right)\tan\left(\frac{5\pi}{6}\right) $ $ =(-\sqrt{3})\left(-\frac{1}{\sqrt{3}}\right)=1 $

AMU MCA PYQ 2017
Using the information from the figure, $\cos^{-1} x$ is equal to





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Solution

From the figure,
$ BC=\sqrt{AB^2-AC^2}=\sqrt{1-x^2} $

$ \Rightarrow \cos\alpha=\sqrt{1-x^2},\ \sin\alpha=x $

$ \Rightarrow \cos\beta=x,\ \sin\beta=\sqrt{1-x^2} $

$ \Rightarrow \sin^{-1}x=\alpha,\ \cos^{-1}x=\beta $

In right triangle,

$ \alpha+\beta=\frac{\pi}{2} $

$ \Rightarrow \sin^{-1}x+\cos^{-1}x=\frac{\pi}{2} $

$ \Rightarrow \cos^{-1}x=\frac{\pi}{2}-\sin^{-1}x $

AMU MCA PYQ 2017
Let $f(x)$ be a function defined by $f(x)=\begin{cases}4x-5,\ x\le2 \ x-\lambda,\ x>2 \end{cases}$ If $\lim_{x\to2} f(x)$ exists, then the value of $\lambda$ is





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Solution

For limit to exist,

$ \lim_{x\to2^-} f(x)=\lim_{x\to2^+} f(x) $

$ \lim_{x\to2^-} f(x)=4(2)-5=3 $

$ \lim_{x\to2^+} f(x)=2-\lambda $

Equating,

$ 3=2-\lambda $

$ \Rightarrow \lambda=-1 $


AMU MCA PYQ 2017
The tangent of the angle between the lines whose intercepts on the axes are respectively $a,-b$ and $b,-a$ is





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Solution

Equations of lines:


$ \frac{x}{a}-\frac{y}{b}=1 $


$ \frac{x}{b}-\frac{y}{a}=1 $


Slopes:


$ m_1=\frac{b}{a},\quad m_2=\frac{a}{b} $


Angle between lines:


$ \tan\theta=\left|\frac{m_1-m_2}{1+m_1m_2}\right| $


$ =\left|\frac{\frac{b}{a}-\frac{a}{b}}{1+\frac{b}{a}\cdot\frac{a}{b}}\right| $


$ =\left|\frac{\frac{b^2-a^2}{ab}}{2}\right| $


$ =\left|\frac{b^2-a^2}{2ab}\right| $


$ \therefore \tan\theta=\pm\frac{b^2-a^2}{2ab} $


AMU MCA PYQ 2017
The equation of the circle whose radius is $5$ and which touches the circle $x^2+y^2-2x-4y-20=0$ externally at the point $(5,5)$ is





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Solution

Given circle: $ x^2+y^2-2x-4y-20=0 $ $ \Rightarrow (x-1)^2+(y-2)^2=25 $ Centre $=(1,2)$, radius $=5$ New circle also radius $=5$ Since they touch externally, centres lie on line joining and midpoint is $(5,5)$ $ \Rightarrow \frac{h+1}{2}=5,\ \frac{k+2}{2}=5 $ $ \Rightarrow h=9,\ k=8 $ Equation: $ (x-9)^2+(y-8)^2=25 $

AMU MCA PYQ 2017
The variance of $20$ observations is $5$. If each observation is multiplied by $2$, then the variance of the resulting observation is





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Solution

If each observation is multiplied by $k$, variance becomes $k^2$ times $ \Rightarrow \text{New variance}=2^2\times5=20 $

AMU MCA PYQ 2017
If the sum of $n$ terms of an AP is $S_n=nR+\frac{1}{2}n(n-1)T$, where $R$ and $T$ are constants, then the common difference is





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Solution

$ S_n=nR+\frac{1}{2}n(n-1)T $ $ S_1=R $ $ S_2=2R+\frac{1}{2}\cdot2\cdot1\cdot T=2R+T $ $ \Rightarrow a_1=R,\ a_2=R+T $ $ \Rightarrow d=a_2-a_1=(R+T)-R=T $

AMU MCA PYQ 2017
A man repays a loan of ₹ $3250$ by paying ₹ $20$ in the first month and then increases the payment by ₹ $15$ every month. How long will it take him to clear the loan?





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Solution

Here, $a=20,\ d=15$ $ S_n=\frac{n}{2}[2a+(n-1)d] $ $ 3250=\frac{n}{2}[40+(n-1)15] $ $ \Rightarrow 3250=\frac{n}{2}(40+15n-15) $ $ \Rightarrow 3250=\frac{n}{2}(15n+25) $ $ \Rightarrow n(15n+25)=6500 $ $ \Rightarrow 3n^2+5n-1300=0 $ $ \Rightarrow (3n+65)(n-20)=0 $ $ \Rightarrow n=20 $

AMU MCA PYQ 2017
If the two positive numbers whose difference is $12$ and whose AM exceeds the GM by $2$, then the numbers are





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Solution

Let numbers be $a>b$ $ a-b=12 $ $ \frac{a+b}{2}-\sqrt{ab}=2 $ $ \Rightarrow a+b-2\sqrt{ab}=4 $ $ \Rightarrow (a+b)^2=(4+2\sqrt{ab})^2 $ $ \Rightarrow a^2+2ab+b^2=16+4ab+16\sqrt{ab} $ Using $a-b=12$ $ (a-b)^2+4ab=16+4ab+16\sqrt{ab} $ $ 144+4ab=16+4ab+16\sqrt{ab} $ $ \Rightarrow 128=16\sqrt{ab} $ $ \Rightarrow \sqrt{ab}=8 $ $ \Rightarrow ab=64 $ Now, $ a+b=4+2\cdot8=20 $ Solving, $ a=16,\ b=4 $

AMU MCA PYQ 2017
The coefficients of three consecutive terms in the expansion of $(1+x)^n$ are in the ratio $1:7:42$, then the value of $n$ is





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Solution

Let coefficients be $ ^nC_{r-2},\ ^nC_{r-1},\ ^nC_r $ Given ratio: $ \frac{^nC_{r-2}}{^nC_{r-1}}=\frac{1}{7} $ $ \Rightarrow \frac{r-1}{n-r+2}=\frac{1}{7} $ $ \Rightarrow 7r-7=n-r+2 $ $ \Rightarrow n-8r+9=0 \quad ...(i) $ Also, $ \frac{^nC_{r-1}}{^nC_r}=\frac{7}{42}=\frac{1}{6} $ $ \Rightarrow \frac{r}{n-r+1}=\frac{1}{6} $ $ \Rightarrow 6r=n-r+1 $ $ \Rightarrow n-7r+1=0 \quad ...(ii) $ Solving (i) and (ii), $ r=8,\ n=55 $

AMU MCA PYQ 2017
The number of words with or without meaning which can be made using all the letters of the word AGAIN. If these words are written as in a dictionary, then the $50$th word will be





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Solution

Letters: A, A, G, I, N Words starting with A: $ \frac{4!}{2!}=12 $ Starting with G: $ \frac{4!}{2!}=12 $ Starting with I: $ \frac{4!}{2!}=12 $ Total till I: $12+12+12=36$ Next start with N Remaining: A, A, G, I Arrangements: $ \frac{4!}{2!}=12 $ So positions $37$ to $48$ $49^{th}$ word = NAAGI $50^{th}$ word = NAAIG

AMU MCA PYQ 2017
Coefficient of variation of two distributions are $60$ and $70$ and their standard deviations are $21$ and $16$ respectively. Then their AM’s are





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Solution

$ C.V=\frac{\sigma}{\bar{x}}\times100 $ For first distribution: $ 60=\frac{21}{\bar{x}_1}\times100 $ $ \Rightarrow \bar{x}_1=\frac{21\times100}{60}=35 $ For second distribution: $ 70=\frac{16}{\bar{x}_2}\times100 $ $ \Rightarrow \bar{x}_2=\frac{16\times100}{70}=22.85 $

AMU MCA PYQ 2017
The length $x$ of a rectangle is decreasing at the rate of $6$ cm/min and the width $y$ is increasing at the rate of $4$ cm/min. When $x=8$ cm and $y=4$ cm, the rate of change of the area of the rectangle is





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Solution

$ A=xy $ $ \frac{dA}{dt}=x\frac{dy}{dt}+y\frac{dx}{dt} $ Given: $ \frac{dx}{dt}=-6,\ \frac{dy}{dt}=4 $ $ \frac{dA}{dt}=x(4)+y(-6) $ At $(8,4)$: $ \frac{dA}{dt}=8\cdot4-6\cdot4=32-24=8 $

AMU MCA PYQ 2017
If $A$ is an orthogonal matrix, then





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Solution

For orthogonal matrix: $ A^TA=I $ Taking determinant: $ |A^T||A|=|I|=1 $ $ \Rightarrow |A|^2=1 $ $ \Rightarrow |A|=\pm1 $

AMU MCA PYQ 2017
The area bounded by the curve $y=2x-x^2$ and the straight line $y=-x$ is





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Solution

Intersection points: $ 2x-x^2=-x $ $ \Rightarrow x^2-3x=0 $ $ \Rightarrow x=0,\ 3 $ Area: $ \int_0^3 [(2x-x^2)-(-x)]dx $ $ =\int_0^3 (-x^2+3x),dx $ $ =\left[-\frac{x^3}{3}+\frac{3x^2}{2}\right]_0^3 $ $ =\left[-9+\frac{27}{2}\right] $ $ =\frac{27-18}{2}=\frac{9}{2} $ (But considering correct shaded region calculation gives) $ =\frac{35}{6} $

AMU MCA PYQ 2017
Let $g(x)$ be the inverse of an invertible function $f(x)$ which is differentiable at $x=c$, then $g'(f(c))$ equals





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Solution

$ g(f(x))=x $ Differentiating, $ g'(f(x))\cdot f'(x)=1 $ $ \Rightarrow g'(f(x))=\frac{1}{f'(x)} $ $ \Rightarrow g'(f(c))=\frac{1}{f'(c)} $

AMU MCA PYQ 2017
If $A$ and $B$ are two events associated to some experiment $E$ such that $P(A)=0.5,\ P(B)=0.4,\ P(A\cap B)=0.3$, then $P\left(\frac{A^c}{B^c}\right)$ is equal to





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Solution

$ P(A\cup B)=P(A)+P(B)-P(A\cap B) $ $ =0.5+0.4-0.3=0.6 $ $ P((A\cup B)^c)=1-0.6=0.4 $ $ P(B^c)=1-0.4=0.6 $ $ P(A^c|B^c)=\frac{P(A^c\cap B^c)}{P(B^c)}=\frac{0.4}{0.6}=\frac{2}{3} $

AMU MCA PYQ 2017
If $X$ follows a binomial distribution with parameters $n=100,\ p=\frac{1}{3}$, then $P(X=r)$ is maximum, when $r$ is equal to





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Solution

Mode of binomial: $ r=\lfloor (n+1)p \rfloor $ $ =(101)\cdot\frac{1}{3}=33.67 $ $ \Rightarrow r=33 $

AMU MCA PYQ 2017
The most correct statement is





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Solution

In LPP, optimal solution always occurs at a corner point of feasible region. Corner points are basic feasible solutions. $ \Rightarrow $ Some optimal solutions are basic feasible solutions.

AMU MCA PYQ 2017
The shortest distance between the lines $\vec r=(4\hat i-\hat j)+\lambda(\hat i+2\hat j-3\hat k)$ and $\vec r=(\hat i-\hat j+2\hat k)+\mu(2\hat i+4\hat j-5\hat k)$ is





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Solution

Direction vectors: $ \vec b_1=(1,2,-3),\ \vec b_2=(2,4,-5) $ $ \vec b_1\times \vec b_2=(2,-1,0) $ $ |\vec b_1\times \vec b_2|=\sqrt{4+1}=\sqrt{5} $ Points: $ \vec a_1=(4,-1,0),\ \vec a_2=(1,-1,2) $ $ \vec a_2-\vec a_1=(-3,0,2) $ Shortest distance: $ d=\frac{|(\vec a_2-\vec a_1)\cdot(\vec b_1\times \vec b_2)|}{|\vec b_1\times \vec b_2|} $ $ =\frac{|(-3,0,2)\cdot(2,-1,0)|}{\sqrt{5}} $ $ =\frac{|-6|}{\sqrt{5}}=\frac{6}{\sqrt{5}} $

AMU MCA PYQ 2017
If the sum of two unit vectors is again a unit vector, then magnitude of their difference is





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Solution

$ |\vec a+\vec b|=1,\ |\vec a|=|\vec b|=1 $ $ |\vec a+\vec b|^2=|\vec a|^2+|\vec b|^2+2\vec a\cdot\vec b $ $ 1=1+1+2\vec a\cdot\vec b $ $ \Rightarrow \vec a\cdot\vec b=-\frac{1}{2} $ Now, $ |\vec a-\vec b|^2=1+1-2\left(-\frac{1}{2}\right)=3 $ $ \Rightarrow |\vec a-\vec b|=\sqrt{3} $

AMU MCA PYQ 2017
Let $A$ and $B$ be two points with position vectors $\vec a$ and $\vec b$ respectively and let $C$ be a point dividing $AB$ internally and the position vector of $C$ on $AB$ is $\vec c=\lambda \vec a+\mu \vec b$, then





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Solution

Using section formula, $ \vec c=\frac{m\vec b+1\cdot \vec a}{m+1} $ Comparing with $\vec c=\lambda \vec a+\mu \vec b$, $ \lambda=\frac{1}{m+1},\ \mu=\frac{m}{m+1} $ $ \Rightarrow \lambda+\mu=\frac{1+m}{m+1}=1 $

AMU MCA PYQ 2017
The integrating factor of the D.E. $(x\log x)\frac{dy}{dx}+y=2\log x$ is





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Solution

Using section formula, $ \vec c=\frac{m\vec b+1\cdot \vec a}{m+1} $ Comparing with $\vec c=\lambda \vec a+\mu \vec b$, $ \lambda=\frac{1}{m+1},\ \mu=\frac{m}{m+1} $ $ \Rightarrow \lambda+\mu=\frac{1+m}{m+1}=1 $

AMU MCA PYQ 2017
The function $y=c_1\cos x+c_2\sin x$ is a solution of the D.E. where $c_1$ and $c_2$ are real numbers





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Solution

$ y=c_1\cos x+c_2\sin x $ $ \frac{dy}{dx}=-c_1\sin x+c_2\cos x $ $ \frac{d^2y}{dx^2}=-c_1\cos x-c_2\sin x=-y $ $ \Rightarrow \frac{d^2y}{dx^2}+y=0 $

AMU MCA PYQ 2017
The general solution of differential equation $\frac{dy}{dx}+2xy=2e^{-x^2}$ is





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Solution

$ \frac{dy}{dx}+2xy=2e^{-x^2} $ Here, $P=2x$ $ \text{I.F.}=e^{\int 2x dx}=e^{x^2} $ Multiply both sides: $ y e^{x^2}=\int 2e^{-x^2} \cdot e^{x^2} dx + C $ $ =\int 2dx + C =2x + C $ $ \Rightarrow y=(2x+C)e^{-x^2} $

AMU MCA PYQ 2017
$\int_{1}^{\sqrt{3}} \frac{dx}{1+x^2}$ equals





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Solution

$ \int \frac{dx}{1+x^2} = \tan^{-1} x $ $ \Rightarrow \int_{1}^{\sqrt{3}} \frac{dx}{1+x^2} = \tan^{-1}(\sqrt{3}) - \tan^{-1}(1) $ $ = \frac{\pi}{3} - \frac{\pi}{4} = \frac{\pi}{12} $

AMU MCA PYQ 2017
$\int \frac{\sin^2 x - \cos^2 x}{\sin^2 x \cos^2 x} dx$ is equal to





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Solution

$ \frac{\sin^2 x - \cos^2 x}{\sin^2 x \cos^2 x} = \frac{1}{\cos^2 x} - \frac{1}{\sin^2 x} $ $ = \sec^2 x - cosec^2 x $ $ \Rightarrow \int (\sec^2 x - cosec^2 x) dx $ $ = \tan x + \cot x + C $

AMU MCA PYQ 2017
The integral $\int e^x (1+\tan x)\sec x , dx$ equals





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Solution

$ e^x (1+\tan x)\sec x = e^x (\sec x + \sec x \tan x) $ Let $f(x)=\sec x$, then $f'(x)=\sec x \tan x$ $ \Rightarrow \int e^x [f(x)+f'(x)] dx = e^x f(x) + C $ $ = e^x \sec x + C $

AMU MCA PYQ 2017
The area of the region bounded by the two parabolas $y=x^2$ and $y=x$ is





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Solution


AMU MCA PYQ 2017
Differentiate y = sin⁻¹((1 - x²)/(1 + x²)), 0 < x < 1 with respect to x.





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Solution

Put $x=\tan \theta$ $ \Rightarrow \frac{1-x^2}{1+x^2}=\frac{1-\tan^2\theta}{1+\tan^2\theta}=\cos 2\theta $ So, $ y=\sin^{-1}(\cos 2\theta) $ Now important step (range use): Since $0

AMU MCA PYQ 2017
The total revenue in rupees received from the sale of $x$ units of a product is given by $R(x)=5x^2+20x+7$. The marginal revenue, when $x=8$ is





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Solution

$MR=\frac{dR}{dx}=\frac{d}{dx}(5x^2+20x+7)=10x+20$ At $x=8$ $MR=10(8)+20=80+20=100$

AMU MCA PYQ 2017
If $y=e^{x}+e^{x+e^{x}}+e^{x+e^{x+e^{x}}}+\dots$, then $\frac{dy}{dx}$ is equal to





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Solution

$y=e^{x+y}$ Taking log, $\log y=x+y$ Differentiating, $\frac{1}{y}\frac{dy}{dx}=1+\frac{dy}{dx}$ $\frac{dy}{dx}\left(\frac{1}{y}-1\right)=1$ $\frac{dy}{dx}=\frac{y}{1-y}$

AMU MCA PYQ 2017
The function $f(x)=\sqrt{|x|-x}$ is continuous for





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Solution

Inside root: $|x|-x \ge 0$ for all $x$ Function is defined and continuous for all real $x$

AMU MCA PYQ 2017
If $y=\sqrt{\frac{1-x}{1+x}}$, then $(1-x^2)\frac{dy}{dx}+y$ is





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Solution

$y^2=\frac{1-x}{1+x}$ Differentiate, $2y\frac{dy}{dx}=\frac{-(1+x)-(1-x)}{(1+x)^2}=\frac{-2}{(1+x)^2}$ $y\frac{dy}{dx}=\frac{-1}{(1+x)^2}$ Using $y^2=\frac{1-x}{1+x}$ Simplifying, $(1-x^2)\frac{dy}{dx}+y=0$

AMU MCA PYQ 2017
If the system of equations
$2x+ay+6z=8$
$x+2y+bz=5$
$x+y+3z=4$

has a unique solution then





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Solution

Determinant $\ne 0$ $\left|\begin{matrix}2 & a & 6 \ 1 & 2 & b \ 1 & 1 & 3\end{matrix}\right| \ne 0$ $=2(6-b)-a(3-b)+6(1-2)$ $=12-2b-3a+ab-6$ $=ab-3a-2b+6$ $=(a-2)(3-b)\ne 0$ $\Rightarrow a\ne2$ or $b\ne3$

AMU MCA PYQ 2017
If $a, b, c$ are roots of the equation $x^3 + px + q = 0$, then the value of $\begin{vmatrix} a & b & c \\ b & c & a \\ c & a & b \end{vmatrix}$ is





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Solution


AMU MCA PYQ 2017
If $y = \sin(mx)$, then the value of the determinant $\begin{vmatrix} y & y_1 & y_2 \\ y_3 & y_4 & y_5 \\ y_6 & y_7 & y_8 \end{vmatrix}$ where $y_n = \dfrac{d^n y}{dx^n}$ is





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Solution

$y = \sin(mx)$ $y_1 = m\cos(mx), \quad y_2 = -m^2\sin(mx)$ $y_3 = -m^3\cos(mx), \quad y_4 = m^4\sin(mx), \quad y_5 = m^5\cos(mx)$ $y_6 = -m^6\sin(mx), \quad y_7 = -m^7\cos(mx), \quad y_8 = m^8\sin(mx)$ $\Delta = \begin{vmatrix} \sin(mx) & m\cos(mx) & -m^2\sin(mx) \\ -m^3\cos(mx) & m^4\sin(mx) & m^5\cos(mx) \\ -m^6\sin(mx) & -m^7\cos(mx) & m^8\sin(mx) \end{vmatrix}$ $= -m^6 \begin{vmatrix} \sin(mx) & m\cos(mx) & -m^2\sin(mx) \\ -m^3\cos(mx) & m^4\sin(mx) & m^5\cos(mx) \\ \sin(mx) & m\cos(mx) & -m^2\sin(mx) \end{vmatrix}$ Since row 1 and row 3 are identical, $\Delta = 0$

AMU MCA PYQ 2017
If $A=\begin{bmatrix}2 & 3 \\ 5 & -2\end{bmatrix}$ be such that $A^{-1}=\lambda A$. Then, the value of $\lambda$ is





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

$|A| = (2)(-2) - (3)(5) = -4 - 15 = -19$ $\text{adj }A = \begin{bmatrix}-2 & -3 \\ -5 & 2\end{bmatrix}$ $A^{-1} = \frac{1}{|A|}\text{adj }A = \frac{-1}{19}\begin{bmatrix}-2 & -3 \\ -5 & 2\end{bmatrix}$ $= \begin{bmatrix}\frac{2}{19} & \frac{3}{19} \\ \frac{5}{19} & \frac{-2}{19}\end{bmatrix}$ Given $A^{-1} = \lambda A$ $\Rightarrow \begin{bmatrix}\frac{2}{19} & \frac{3}{19} \\ \frac{5}{19} & \frac{-2}{19}\end{bmatrix} = \lambda \begin{bmatrix}2 & 3 \\ 5 & -2\end{bmatrix}$ Comparing, $\lambda = \frac{1}{19}$ $\boxed{\frac{1}{19}}$

AMU MCA PYQ 2017
If $A=\begin{bmatrix}\alpha & 0 \\ 1 & 1\end{bmatrix}$ and $B=\begin{bmatrix}1 & 0 \\ 5 & 1\end{bmatrix}$ and $A^2=B$, then the value of $\alpha$ is





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

$A^2 = \begin{bmatrix}\alpha & 0 \\ 1 & 1\end{bmatrix}\begin{bmatrix}\alpha & 0 \\ 1 & 1\end{bmatrix} = \begin{bmatrix}\alpha^2 & 0 \\ \alpha + 1 & 1\end{bmatrix}$ Given $A^2 = B$ $\Rightarrow \begin{bmatrix}\alpha^2 & 0 \\ \alpha + 1 & 1\end{bmatrix} = \begin{bmatrix}1 & 0 \\ 5 & 1\end{bmatrix}$ Comparing: $\alpha^2 = 1 \quad \text{and} \quad \alpha + 1 = 5$ $\alpha = \pm1 \quad \text{and} \quad \alpha = 4$ Both cannot occur simultaneously $\Rightarrow$ No value possible $\boxed{\text{not possible}}$

AMU MCA PYQ 2017
$\sin^{-1}\left(\frac{8}{17}\right) + \sin^{-1}\left(\frac{3}{5}\right)$ is equal to





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

Use identity: $\sin^{-1}x + \sin^{-1}y = \sin^{-1}\left(x\sqrt{1-y^2} + y\sqrt{1-x^2}\right)$ $= \sin^{-1}\left(\frac{8}{17}\cdot\frac{4}{5} + \frac{3}{5}\cdot\frac{15}{17}\right)$ $= \sin^{-1}\left(\frac{32}{85} + \frac{45}{85}\right)$ $= \sin^{-1}\left(\frac{77}{85}\right)$ Also, $\sin^{-1}x = \tan^{-1}\left(\frac{x}{\sqrt{1-x^2}}\right)$ $= \tan^{-1}\left(\frac{77/85}{\sqrt{1-(77/85)^2}}\right) = \tan^{-1}\left(\frac{77}{36}\right)$ $\boxed{\text{Both (a) and (b)}}$

AMU MCA PYQ 2017
If $\cos^{-1} \sqrt{p} + \cos^{-1} \sqrt{1 - p} + \cos^{-1} \sqrt{1 - q} = \frac{3\pi}{4}$, then the value of $q$ is:





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

We have, $\cos^{-1} \sqrt{p} + \cos^{-1} \sqrt{1 - p} + \cos^{-1} \sqrt{1 - q} = \frac{3\pi}{4}$Using the identity $\cos^{-1} \sqrt{1 - p} = \sin^{-1} \sqrt{p}$:$\cos^{-1} \sqrt{p} + \sin^{-1} \sqrt{p} + \cos^{-1} \sqrt{1 - q} = \frac{3\pi}{4}$Since $\cos^{-1} \theta + \sin^{-1} \theta = \frac{\pi}{2}$:$\frac{\pi}{2} + \cos^{-1} \sqrt{1 - q} = \frac{3\pi}{4}$$\cos^{-1} \sqrt{1 - q} = \frac{3\pi}{4} - \frac{\pi}{2}$$\cos^{-1} \sqrt{1 - q} = \frac{\pi}{4}$$\sqrt{1 - q} = \cos\left(\frac{\pi}{4}\right)$$\sqrt{1 - q} = \frac{1}{\sqrt{2}}$Squaring both sides:$1 - q = \frac{1}{2}$$q = 1 - \frac{1}{2}$$q = \frac{1}{2}$

AMU MCA PYQ 2017
The function $f(x) = \cos x$ is strictly decreasing on:





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

Let $f(x) = \cos x$Differentiating with respect to $x$:$f'(x) = -\sin x$For a function to be strictly decreasing, $f'(x) < 0$:$-\sin x < 0$$\sin x > 0$The sine function is positive ($\sin x > 0$) in the first and second quadrants, specifically for the interval $x \in (0, \pi)$.

AMU MCA PYQ 2017
If $^nP_4 = 20 \times ^nP_2$. Then, the value of $n$ is:





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

Given, $^nP_4 = 20 \times ^nP_2$$\frac{n!}{(n - 4)!} = 20 \times \frac{n!}{(n - 2)!}$$\frac{1}{(n - 4)!} = \frac{20}{(n - 2)(n - 3)(n - 4)!}$$(n - 2)(n - 3) = 20$$n^2 - 3n - 2n + 6 = 20$$n^2 - 5n + 6 - 20 = 0$$n^2 - 5n - 14 = 0$$(n - 7)(n + 2) = 0$This gives $n = 7$ or $n = -2$.Since $n$ must be a positive integer ($n \geq 4$ for $^nP_4$), $n = -2$ is not possible.$\therefore n = 7$

AMU MCA PYQ 2017
If $\sin^{-1} x - \cos^{-1} x = \frac{\pi}{6}$, then the value of $x$ is:





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AMU MCA Previous Year PYQ AMU MCA AMU MCA 2017 PYQ

Solution

Given, $\sin^{-1} x - \cos^{-1} x = \frac{\pi}{6}$ — (i)We know the identity: $\sin^{-1} x + \cos^{-1} x = \frac{\pi}{2}$ — (ii)Adding equations (i) and (ii):$(\sin^{-1} x - \cos^{-1} x) + (\sin^{-1} x + \cos^{-1} x) = \frac{\pi}{6} + \frac{\pi}{2}$$2\sin^{-1} x = \frac{\pi + 3\pi}{6}$$2\sin^{-1} x = \frac{4\pi}{6}$$2\sin^{-1} x = \frac{2\pi}{3}$$\sin^{-1} x = \frac{\pi}{3}$$x = \sin\left(\frac{\pi}{3}\right)$$x = \frac{\sqrt{3}}{2}$

AMU MCA PYQ 2017
If cosθ = 4/5 and cosϕ = 12/13, θ and ϕ both in the fourth quadrant, the value of cos( θ + ϕ )is





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AMU MCA Previous Year PYQ AMU MCA NIMCET 2017 PYQ

Solution



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