Question

1.先化简再求值：（x+3 - 7/x-3）÷（ x²/2x-6 - 4x-8/x-3),其中x=2^-3

Answer 1

= [(x+3)(x-3)-7]/(x-3) 2(x-3)/(x²-8x+4²)

= 2 (x²-4²) / (x-4)²

=2(x+4)(x-4)/(x-4)²

=2(x+4)/(x-4)

当x=2^-3=1/8时

原式=2(1/4+4)/(1/4-4)

=-66/31