Question

Find the value of k if: (2x − y)² − (2x + y)² = 4xyk​

Answer 1

k = - 2

Explanation:

( 2x - y )²

Formula : -

( a - b )² = a² + b² - 2ab

Here,

a = 2x

b = y

( 2x - y )²

= ( 2x )² + y² - 2 ( 2x ) ( y )

= 4x² + y² - 4xy

So,

( 2x - y )² = 4x² + y² - 4xy

( 2x + y )²

Formula : -

( a + b )² = a² + b² + 2ab

Here,

a = 2x

b = y

( 2x + y )²

= ( 2x )² + y² + 2 ( 2x ) ( y )

= 4x² + y² + 4xy

So,

( 2x + y )² = 4x² + y² + 4xy

( 2x - y )² - ( 2x + y )²

= 4x² + y² - 4xy - ( 4x² + y² + 4xy )

= 4x² + y² - 4xy - 4x² - y² - 4xy

= 4x² - 4x² + y² - y² - 4xy - 4xy

= 0 + 0 - 8xy

= - 8xy

( 2x - y )² - ( 2x + y )² = 4xyk

- 8xy = 4xyk

Divide 4xy on both sides,

- 8xy / 4xy = 4xyk / 4xy

- 2 = k

k = - 2

Therefore, the value of k is - 2.