Question

(a+b)(a-b)+(b+c)(b-c)+(c+a)(c-a)

Answer 1

a*2-b*2+ b*2-c*2+c*2-a*2
=0

Answer 2

${a}^{2} - {b}^{2} + {b}^{2} - {c}^{2} + {c}^{2} - {a}^{2} \: = \: 0$