Question

1、先化简在求值:(x-4)(x-3)-2(x+6)(x-5)其中x=-1

Answer 1

解

(x-4)(x-3)-2(x+6)(x-5)

=(x²-7x+12)-2(x²+x-30)

=(x²-2x²)+(-7x-2x)+(12+60)

=-x²-9x+72

=-1+9+72

=80

选择1/2a²+2a和1/2a²-a

(1/2a²+2a)(1/2a²-a)

=1/4a^4-1/2a³+a³-2a²

=1/4a^4+1/2a³-2a²