Question

( 7x -9y) ( 7x - 9y) find using suitable identity

Answer 1

we need to use (7x - 9y)*2
(a - b) *2=a*2-2ab+b*2
a=7x
b=9y
(7x)2-2(7x)(9y) +(9y) 2
=49x*2-126xy+81y*2