Answer:
k = - 2
Step-by-step 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.
