约分8m-2m²/m²-16 x²-1/3-6x+3x²

(8m-2m²)/(m²-16)
=2m(4-m) / (m+4)(m-4)
=-2m/(m+4)
(x²-1)/(3-6x+3x²)
=(x+1)(x-1) / 3(x-1)²
=(x+1)/3(x-1)先化简分式（a+b)²-6（a+b)+9/(a+b)²-9再求值，其中a+b=-½把a+b看作一个数；把3/(a+b)看作一个数；（a+b)²-6（a+b)+9/(a+b)²-9=[(a+b)-3/(a+b)]²+6-6（a+b)-9=[-1/2 -3(-2)]²-6(-1/2)-3=[11/2]²+3-3=121/4