Question

(a + b - c) (a - b + c)​

Answer 1

Answer:

$(a + b -c)(a - b + c) \\ a(a - b + c) + b(a - b + c) - c(a - b + c) \\ a {}^{2} - ab + ac + ab - b {}^{2} + bc - ac + bc - c {}^{2} \\ a { }^{2} - b {}^{2} - c {}^{2}$

so your answer is here