Qus : 3
CUET UG Mathematics Applied PYQ
3
The value of$\mathbf{i}\cdot(\mathbf{j}\times\mathbf{k})+\mathbf{j}\cdot(\mathbf{i}\times\mathbf{k})+\mathbf{k}\cdot(\mathbf{i}\times\mathbf{j})$is:
1
0 2
-1 3
1 4
3 Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution Using vector identities:
$\mathbf{i}\times\mathbf{j}=\mathbf{k}$
$\mathbf{j}\times\mathbf{k}=\mathbf{i}$
$\mathbf{k}\times\mathbf{i}=\mathbf{j}$
First term
$\mathbf{i}\cdot(\mathbf{j}\times\mathbf{k})$
$=\mathbf{i}\cdot\mathbf{i}=1$
Second term
$\mathbf{j}\cdot(\mathbf{i}\times\mathbf{k})$
But
$\mathbf{i}\times\mathbf{k}=-\mathbf{j}$
So
$\mathbf{j}\cdot(-\mathbf{j})=-1$
Third term
$\mathbf{k}\cdot(\mathbf{i}\times\mathbf{j})$
$=\mathbf{k}\cdot\mathbf{k}=1$
Adding
$1-1+1=1$
Qus : 6
CUET UG Mathematics Applied PYQ
3
The equation of plane passing through the point $(0,7,-7)$ and containing the line
$\frac{x+1}{-3}=\frac{y-3}{2}=\frac{z+2}{1}$
is:
1
$x-y-z=0$ 2
$4x+y+z=0$ 3
$x+y+z=0$ 4
$4x-y-z=0$ Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution
The line
$\frac{x+1}{-3}=\frac{y-3}{2}=\frac{z+2}{1}$
gives a point on the line
$(-1,3,-2)$
Direction vector of line
$\vec d=(-3,2,1)$
Vector joining given point and line point
$(0,7,-7)-(-1,3,-2)=(1,4,-5)$
Normal vector of plane
$\vec n = \vec d \times (1,4,-5)$
$\vec n=
\begin{vmatrix}
\mathbf{i} & \mathbf{j} & \mathbf{k} \\
-3 & 2 & 1 \\
1 & 4 & -5
\end{vmatrix}$
$= -14\mathbf{i}-14\mathbf{j}-14\mathbf{k}$
Normal vector $\propto (1,1,1)$
Plane equation
$x+y+z+d=0$
Substitute point $(0,7,-7)$
$0+7-7+d=0$
$d=0$
Plane
$x+y+z=0$
Qus : 7
CUET UG Mathematics Applied PYQ
2
A line
$\frac{x-2}{1}=\frac{y-3}{2}=\frac{z-1}{-1}$
is perpendicular to a plane $(P)$ which passes through the point $(4,3,9)$.
If the mirror image of point $S$ on the line $(L)$ in the given plane $(P)$ is $(2,3,1)$, then coordinates of point $S$ is:
1
$(1,0,3)$ 2
$(0,-1,3)$ 3
$(-2,-3,-1)$ 4
$(4,7,-1)$ Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution Direction ratios of line
$\vec n=(1,2,-1)$
Since the line is perpendicular to the plane, this vector is the **normal vector of the plane**.
Plane passing through $(4,3,9)$
Equation
$1(x-4)+2(y-3)-1(z-9)=0$
$x+2y-z-1=0$
Mirror image property:
The plane is the midpoint between $S$ and its image.
Image point
$S'=(2,3,1)$
Parametric form of line
$x=2+t$
$y=3+2t$
$z=1-t$
So any point on the line
$S=(2+t,3+2t,1-t)$
Midpoint between $S$ and $S'$
$\left(\frac{2+t+2}{2},\frac{3+2t+3}{2},\frac{1-t+1}{2}\right)$
$=\left(2+\frac{t}{2},3+t,1-\frac{t}{2}\right)$
Substitute into plane
$x+2y-z-1=0$
$\left(2+\frac{t}{2}\right)+2(3+t)-\left(1-\frac{t}{2}\right)-1=0$
$6+3t=0$
$t=-2$
Hence
$S=(2-2,3-4,1+2)$
$S=(0,-1,3)$
Qus : 8
CUET UG Mathematics Applied PYQ
2
A ball is thrown upwards from the plane surface of the ground.
Suppose the plane surface from which the ball is thrown consists of the points
$A(1,0,2),\; B(3,-1,1)$ and $C(1,2,1)$ on it.
The highest point of the ball takes is $D(2,3,1)$ as shown in the figure.
Using this information answer the question.
1
$3x-2y+4z=-11$ 2
$3x+2y+4z=11$ 3
$3x-2y-4z=11$ 4
$-3x+2y+4z=-11$ Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution Points
$A(1,0,2)$
$B(3,-1,1)$
$C(1,2,1)$
Direction vectors
$\vec{AB}=(3-1,-1-0,1-2)=(2,-1,-1)$
$\vec{AC}=(1-1,2-0,1-2)=(0,2,-1)$
Normal vector of plane
$\vec{n}=\vec{AB}\times\vec{AC}$
$\vec{n}=
\begin{vmatrix}
\mathbf{i} & \mathbf{j} & \mathbf{k}\\
2 & -1 & -1\\
0 & 2 & -1
\end{vmatrix}$
$=3\mathbf{i}+2\mathbf{j}+4\mathbf{k}$
So normal vector
$(3,2,4)$
Equation of plane
$3(x-1)+2(y-0)+4(z-2)=0$
$3x+2y+4z-11=0$
$3x+2y+4z=11$
Qus : 9
CUET UG Mathematics Applied PYQ
1
A ball is thrown upwards from the plane surface of the ground.
Suppose the plane surface from which the ball is thrown consists of the points
$A(1,0,2),\; B(3,-1,1)$ and $C(1,2,1)$ on it.
The highest point of the ball takes is $D(2,3,1)$ as shown in the figure.
Using this information answer the question.
The maximum height of the ball from the ground is:
1
$\frac{5}{\sqrt{29}}$ units 2
$\frac{7}{\sqrt{29}}$ units 3
$\frac{6}{\sqrt{29}}$ units 4
$\frac{8}{\sqrt{29}}$ units Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution Equation of plane through $A,B,C$
$3x+2y+4z=11$
Maximum height of the ball = perpendicular distance of point $D(2,3,1)$ from the plane.
Distance formula
$d=\frac{|Ax_1+By_1+Cz_1+D|}{\sqrt{A^2+B^2+C^2}}$
Plane
$3x+2y+4z-11=0$
Substitute $D(2,3,1)$
$=|3(2)+2(3)+4(1)-11|$
$=|6+6+4-11|$
$=|5|$
Denominator
$\sqrt{3^2+2^2+4^2}$
$=\sqrt{9+4+16}$
$=\sqrt{29}$
Therefore
$d=\frac{5}{\sqrt{29}}$
Qus : 10
CUET UG Mathematics Applied PYQ
3
A ball is thrown upwards from the plane surface of the ground.
Suppose the plane surface from which the ball is thrown consists of the points
$A(1,0,2),\; B(3,-1,1)$ and $C(1,2,1)$ on it.
The highest point of the ball takes is $D(2,3,1)$ as shown in the figure.
Using this information answer the question.
The equation of the perpendicular line drawn from the maximum height of the ball to the ground is:
1
$\frac{x-1}{2}=\frac{y+3}{1}=\frac{z-5}{-2}$ 2
$\frac{x-2}{-3}=\frac{y-3}{2}=\frac{z-1}{-4}$ 3
$\frac{x-2}{3}=\frac{y-3}{2}=\frac{z-1}{4}$ 4
$\frac{x+1}{-2}=\frac{y+3}{-1}=\frac{z-5}{2}$ Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution Ground plane passes through points
$A(1,0,2),\; B(3,-1,1),\; C(1,2,1)$
Direction vectors
$\vec{AB}=(2,-1,-1)$
$\vec{AC}=(0,2,-1)$
Normal vector of plane
$\vec{n}=\vec{AB}\times\vec{AC}$
$\vec{n}=
\begin{vmatrix}
\mathbf{i}&\mathbf{j}&\mathbf{k}\\
2&-1&-1\\
0&2&-1
\end{vmatrix}
$
$=3\mathbf{i}+2\mathbf{j}+4\mathbf{k}$
So direction ratios of perpendicular line
$(3,2,4)$
The perpendicular line passes through point
$D(2,3,1)$
Hence equation of line
$\frac{x-2}{3}=\frac{y-3}{2}=\frac{z-1}{4}$
Qus : 11
CUET UG Mathematics Applied PYQ
3
A ball is thrown upwards from the plane surface of the ground.
Suppose the plane surface from which the ball is thrown consists of the points
$A(1,0,2),\; B(3,-1,1)$ and $C(1,2,1)$ on it.
The highest point of the ball takes is $D(2,3,1)$ as shown in the figure.
Using this information answer the question.
The coordinates of the foot of the perpendicular drawn from the maximum height of the ball to the ground are:
1
$\left(\frac{43}{29},-\frac{77}{29},-\frac{9}{29}\right)$ 2
$\left(\frac{9}{7},-\frac{1}{7},-\frac{10}{7}\right)$ 3
$\left(\frac{43}{29},\frac{77}{29},\frac{9}{29}\right)$ 4
$\left(-\frac{13}{29},-\frac{7}{29},\frac{19}{29}\right)$ Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution Plane through points $A,B,C$
$3x+2y+4z=11$
Normal vector of plane
$\vec{n}=(3,2,4)$
Point
$D(2,3,1)$
Foot of perpendicular formula
$\left(x_1-\frac{a(ax_1+by_1+cz_1+d)}{a^2+b^2+c^2},\;
y_1-\frac{b(ax_1+by_1+cz_1+d)}{a^2+b^2+c^2},\;
z_1-\frac{c(ax_1+by_1+cz_1+d)}{a^2+b^2+c^2}\right)$
Plane
$3x+2y+4z-11=0$
Substitute point $D$
$3(2)+2(3)+4(1)-11$
$=6+6+4-11$
$=5$
Denominator
$3^2+2^2+4^2$
$=9+4+16$
$=29$
Coordinates of foot
$x=2-\frac{3(5)}{29}=\frac{43}{29}$
$y=3-\frac{2(5)}{29}=\frac{77}{29}$
$z=1-\frac{4(5)}{29}=\frac{9}{29}$
Foot of perpendicular
$\left(\frac{43}{29},\frac{77}{29},\frac{9}{29}\right)$
Qus : 12
CUET UG Mathematics Applied PYQ
4
A ball is thrown upwards from the plane surface of the ground.
Suppose the plane surface from which the ball is thrown consists of the points
$A(1,0,2),\; B(3,-1,1)$ and $C(1,2,1)$ on it.
The highest point of the ball takes is $D(2,3,1)$ as shown in the figure.
Using this information answer the question.
The area of $\triangle ABC$ is:
1
$\sqrt{29}$ sq. units 2
$\frac{1}{4}\sqrt{29}$ sq. units 3
$\frac{1}{16}\sqrt{29}$ sq. units
4
$\frac{1}{2}\sqrt{29}$ sq. units
Go to Discussion
CUET UG Mathematics Applied Previous Year PYQ
CUET UG Mathematics Applied CUET UG 2022 Applied Mathematics PYQ
Solution
$A(1,0,2)$
$B(3,-1,1)$
$C(1,2,1)$
Vectors
$\vec{AB}=(3-1,-1-0,1-2)=(2,-1,-1)$
$\vec{AC}=(1-1,2-0,1-2)=(0,2,-1)$
Cross product
$\vec{AB}\times\vec{AC}$
$=
\begin{vmatrix}
\mathbf{i}&\mathbf{j}&\mathbf{k}\\
2&-1&-1\\
0&2&-1
\end{vmatrix}
$
$=3\mathbf{i}+2\mathbf{j}+4\mathbf{k}$
Magnitude
$|\vec{AB}\times\vec{AC}|$
$=\sqrt{3^2+2^2+4^2}$
$=\sqrt{29}$
Area of triangle
$=\frac{1}{2}|\vec{AB}\times\vec{AC}|$
$=\frac{1}{2}\sqrt{29}$
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