Question

先约分,再求值：（1）1-4x四次方/2x的三次方+x,其中x=-2

Answer 1

1-4x四次方/2x的三次方+x

=(1-2x²)(1+2x²)/x(2x²+1）

=(1-2x²)/x

=(1-8)/(-2)

=7/2

(2)x²y-2xy+y/y-x²y,其中x=-2；

原式=y(x-1)²/y(1+x)(1-x)

=1-x/(1+x)

=3/(-1)

=-3

（3）a²-3ab/a²-6ab+9b²,其中a=3/2,b=-2/3

原式=a(a-3b)/(a-3b)²

=a/(a-3b)

=3/2 ÷ (3/2+2)

=3/2×2/7

=3/7