Read, remember and use the following :
(a + b)2 = a2 + ab + ab + b2
= a2 + 2ab + b2
(first term sign second term)2 = (first term)2 (sign) 2(first term)(second term) + (second term)2
(a sign b)2 = (a)2 (sign) 2(a)(b) + (b)2