三个多项式的乘法 要简便算法1.（a-b+2)（a+b-2)2.（x-1)²（x+1)²（x²+1）²3.(2x+y-1）²

1.原式=[a-(b-2)][a+(b-2)]=a^2-(b-2)^2=a^2-b^2+4-4b
2.原式=[(x-1)(x+1)(x^2+1)]^2=[(x^2-1)(x^2+1)]^2=(x^4-1)^2=x^8+1-2x^2

1: -[(b-2)-a][(b-2)+a]=-(b-2)^2-a^2
2:](x-1)(x+1)]^2*(x^2+1)^2=(x^2-1)^2*(x^2+1)^2=(x^4-1)^2
3:就直接算吧

1.（a-b+2)（a+b-2)
=[a-(b-2)][a+(b-2)]
=a²-(b-2)²
=a²-b²+4b-4
2.（x-1)²（x+1)²（x²+1）²
=(x²-1)²(x²+1)²
=(x^4-1)²
=x^8-2x^4+1
3.(2x+y-1）²
=[(2x+y)-1]²
=(2x+y)²-2(2x+y)+1²
=4x²+4xy+y²-4x-2y+1