# If 3x + 5y = 11 and Xy = 2, Find the Value of 9x2 + 25y2 - Mathematics

If 3x + 5y = 11 and xy = 2, find the value of 9x2 + 25y2

#### Solution

We have:

$\left( 3x + 5y \right)^2 = \left( 3x \right)^2 + 2\left( 3x \right)\left( 5y \right) + \left( 5y \right)^2$

$\Rightarrow \left( 3x + 5y \right)^2 = 9 x^2 + 30xy + 25 y^2$

$\Rightarrow 9 x^2 + 25 y^2 = \left( 3x + 5y \right)^2 - 30xy$

$\Rightarrow 9 x^2 + 25 y^2 = {11}^2 - 30 \times 2$     ($\because$ $3x + 5y = 11 \text { and } xy = 2$)

$\Rightarrow 9 x^2 + 25 y^2 = 121 - 60$

$\Rightarrow 9 x^2 + 25 y^2 = 61$

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#### APPEARS IN

RD Sharma Class 8 Maths
Chapter 6 Algebraic Expressions and Identities
Exercise 6.6 | Q 12 | Page 44