Question

Expand following, using suitable identities :- (3a – 7b – c)² 

Answer 1

It is known that,

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

(3a – 7b – c)² = (3a)² + (-7b)² + (-c)² + 2(3a)(-7b) + 2(-7b)(-c) + 2(-c)(3a)

                     = 9a² + 49b² + c² - 42ab + 14bc - 6ac