Question

Expand following, using suitable identities :- (x + 2y + 4z)² 

Answer 1

It is known that,

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

(x + 2y + 4z)² = x² + (2y)² + (4z)² + 2(x)(2y) + 2(2y)(4z) + 2(4z)(x)

                      = x² + 4y² + 16z² + 4xy + 16yz + 8xz