Question

expand of the following using suitable identity (3a-7b-c)square sorry is math question

Answer 1

using the identity:
${(a - b - c) }^{2} = {a}^{2} + {b}^{2} + {c }^{2} - 2ab + 2bc - 2ca$


Substitute the values

${(3a)}^{2} + {(7b)}^{2} + {(c)}^{2} - 2(3a)(7b) + 2(7b)(c) - 2(c)(3a)$
which equals to:
${9a}^{2} + {49b}^{2} + {c}^{2} - 42ab + 14bc - 6ac$
is the answer.