Question

expand (3a-7b-c)square using suitable identity

Answer 1

identity is (a+b+c)whole square = a^2+b^2+c^2+2ab+2bc+2ca

now expand it by putting a = 3a, b = (-7b), c= (-c)

substitute the values and you will get the answer

= 9a^2+49b^2+c^2-42ab+14bc-6ca

Answer 2

Concept

Recall the formula we will use to solve the question.

(a+b+c)² = a² + b² + c²+ 2ab + 2bc + 2ac

Given

The expression (3a-7b-c)².

To find

We have to expand the given expression.

Solution

The expression is (3a-7b-c)²

Apply the formula

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

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

Hence the expand value is 9a²+49b²+c²-42ab+14bc-6ac.