(a + b + c)(ab + bc + ca) - abc
= $$a^2b + a^2c + ab^2 + cb^2 + bc^2 + ac^2 + 2abc$$
= $$a^2(b +c)+bc(b+c)+a(b^2+c^2+2bc)$$
= $$a^2(b+c)+bc(b+c)+a(b+c)^2$$
=$$(b+c)(a^2+bc+ab+ac)$$
= (b + c)[a(a + b) + c(a + b)]
= (a + b)(b + c)(c + a)
Create a FREE account and get: