7p²-(p+1)(p+2) = 7p²-(p²+3p+2) = 7p²-p²-3p-2 = 6p²-3p-2
(a+2)(a-1)-(a+1)(a-2)= a²+a-2-(a+1)(a-2) = a²+a-2-(a²-a-2) = a²+a-2-(a²-a-2) =
a²+a-2-a²+a+2 = 2a
(p+2)(p-1)+(p+3)(p-5) = p²+p-2+(p+3)(p-5) = p²+p-2+p²-2p-15 = 2p²+p-2-2p-15 =
2p²-p-2-15 = 2p²-p-17
(4-x)(2-x)-(x+2)(1-x)= 8-6x+x²-(x+2)(1-x) = 8-6x+x²-(-x-x²+2) =
8-6x+x²+x+x²-2 = 8-5x+x²+x²-2 = 8-5x+2x²-2 = 6-5x+2x²