If (x+y)=3, x y=2, then what is the value of x³+ y³ ? · ABC26GN1225

Subject: General Aptitude · Chapter: Simplification

If $(x+y)=3, x y=2$, then what is the value of $x^{3}+$ $y^{3}$ ?
(a)6
(b)7
(c)8
(d)9
(e)None of these
Answer
Answer (as printed): D
Explanation
$(x+y)=3 \Rightarrow(x+y)^{2}=9$ $$\begin{aligned} & \Rightarrow x^{2}+y^{2}+2 x y=9 \\ & \Rightarrow x^{2}+y^{2}=9-2 x y=9-4=5 . \end{aligned} \begin{aligned} \therefore x^{3}+y^{3} & =(x+y)\left(x^{2}+y^{2}-x y\right)=3(5-2) \\ & =3 \times 3=9 \cdot\left[\because x+y=3, x^{2}+y^{2}=5, x y=2\right] \end{aligned}$$

Explanation as extracted from the printed page; notation may be imperfect.

Study loop for Simplification

1. Practise the PYQsPrevious-year questions, with answers

· Browse this chapter in the app