计算.⑴﹙5x²-7x+4﹚﹙7x-6﹚.⑵﹙2x-1﹚﹙4x²+2x+1﹚.⑶﹙a+b-c﹚﹙a-
1个回答

(1)原式=35x³-79x²+70x-24

(2)原式=(2x)³-(1)³=8x³-1.利用立方差公式x³-y³=(x-y)(x²+xy+y²)

(3)原式=(a-c)²-b²=a²-b²+c²-2ac.利用平方差公式x²-y²=(x-y)(x+y)

(4)原式=(2x-3y)²-z²=4x²+9y²-z²-12xy.利用平方差公式x²-y²=(x-y)(x+y)

(5)原式=(x²-9)(x²+9)=x^4-81

(6)原式=(x-y+x+y)[(x-y)²-(x-y)(x+y)+(x+y)²]

=2x[x²+3y²]

=2x³+6xy².利用立方和公式x³+y³=(x+y)(x²-xy+y²)