Question

a(a+b+c)+b(a+b+c)+c(a+b+c)-4c^2
помощь

Answer 1

(a+b+c)(a+b+c)-4c^2=(a+b+c)^2-(2c)^2=(a+b+c+2c)(a+b+c-2c)=(a+b+3c)(a+b-c)