(5a+7b)²-70ab = 25a²+70ab+49b²-70ab = 25a²+49b²
(x-8)²-2x(6-x)² = x²-16x+64-2x(36-12x+x²) = x²-16x+64-72x+24x²-2x3=2x3+25x²-8x+64
-6(2x-y)²= -6(4x²-4xy+y²)= -24x²+24xy-6y²
(5+y)²+y(y-7) =25+10y+y²+y²-7y=2y²+3y+25
9b²-(a-3b)²=9b²-a²-6ba+9b² =18b²-a²-6ba
