Aspire's Library

A Place for Latest Exam wise Questions, Videos, Previous Year Papers,
Study Stuff for MCA Examinations - NIMCET

Previous Year Question (PYQs)



Given the equation $x+y =1$, $x^2+y^2 =2$, $x^5 +y^5 =A$. Let N be the number of solution pairs (x,y) to this system of equations. Then AN is equal to





Solution

From \(x+y=1\) and \(x^2+y^2=2\): $(x+y)^2=x^2+y^2+2xy$
\[ \;\Rightarrow\; 1=2+2xy \;\Rightarrow\; xy=-\tfrac12. \] Thus \(x,y\) are roots of \(t^2 - t - \tfrac12=0\), giving two ordered pairs \((x,y)\). Hence \(N=2\). Let \(p_n=x^n+y^n\). For quadratic roots with \(s_1=x+y=1\) and \(s_2=xy=-\tfrac12\), \[ p_n = s_1 p_{n-1} - s_2 p_{n-2} \quad (n\ge2), \] with \(p_0=2,\; p_1=1\). \[ p_2=1\cdot1-(-\tfrac12)\cdot2=2,\quad\] $$ p_3=1\cdot2-(-\tfrac12)\cdot1=\tfrac52,$$ \[ p_4=\tfrac72,\quad p_5=1\cdot\tfrac72-(-\tfrac12)\cdot\tfrac52=\tfrac{19}{4}. \] Therefore \(A=p_5=\tfrac{19}{4}\). With \(N=2\), \[ AN=\frac{19}{4}\cdot 2=\boxed{\tfrac{19}{2}}. \]
✅ Final Answer: \(AN=\dfrac{19}{2}\)


Online Test Series,
Information About Examination,
Syllabus, Notification
and More.

Click Here to
View More


Online Test Series,
Information About Examination,
Syllabus, Notification
and More.

Click Here to
View More

Ask Your Question or Put Your Review.

loading...