(x+3)(x-3)=x²-3x+3x-9=x²-9
(3x+2y)²=9x²+12xy+4y²
(a-2)²=a²-4a+4
25-b²=(5-b)(5+b)
a(a+5)-(a-b)(a+b)=a²+5a-(a²+ab-ab-b²)=a²+5a-a²+b²=5a+b²
(x+2)(x-6)-(5-x)²=x²-6x+2x-12-(25-10x+x²)=x²-4x-12-25+10x-x²=6x-27
4ab-2b²+2(a-b)²=4ab-2b²+2(a²-2ab+b²)=4ab-2b²+2a²-4ab+2b²=+2a²