Show that

i)(a − b)(a + b) = a^2 − b^2

ii)(a + b)2 = a^2 + 2ab + b^2

iii)(a − b)2 = a^2 − 2ab + b^2

iv)(a + b)3 = a^3 + 3a^2b + 3ab^2 + b^3