Proving Fundamental Algebraic Identities and Equalities

Prove the following equalities:**
a) $(a + b)^2 = a^2 + 2ab + b^2$
b) $(a - b)^2 = a^2 - 2ab + b^2$
c) $(a + b + c)^2 = a^2 + b^2 + c^2 + 2ab + 2ac + 2bc$
d) $a^2 - b^2 = (a + b)(a - b)$