Question

evaluate 1/7(9x^2 + 12y^2) (9x^2-12y^2), if x = 1 and y = -1​

Answer 1

Answer:

-9

Step-by-step explanation:

Given: x = 1

           y = - 1

Putting the values of x and y in their respective places,

⇒ 1/7  [9 ( 1 )^2 + 12 ( -1 )^2] [9 ( 1 )^2 - 12 ( -1 )^2]

⇒ 1/7  ( 9 + 12 ) ( 9 - 12 )

Using the identity ( a + b ) ( a - b ) = $a^2 - b^2$

⇒ 1/7 ( 9^2 - 12^2 )

⇒ 1/7 ( 81 - 144 )

⇒ 1/7 × -63

⇒ - 9