Question

Expand following, using suitable identities :- (–2x + 5y – 3z)² 

Answer 1

It is known that,

(x + y + z)² = x² + y² + z² + 2xy + 2yz + 2zx

(–2x + 5y – 3z)² = (-2x)² + (5y)² + (-3z)² + 2(-2x)(5y) + 2(5y)(-3z) + 2(-3z)(-2x)

                         = 4x² + 25y² + 9z² - 20xy - 30yz +12xz