化简x²-3x/9-x²和a²+ab/a²-b²

化简x²-3x/9-x²和a²+ab/a²-b²

(x²-3x)/(9-x²)
=x(x-3)/(3+x)(3-x)
=-x/(x+3)
(a²+ab)/(a²-b²)
=a(a+b)/(a+b)(a-b)
=a/(a-b)

f'(x)=3x^2-6ax+2b 则有 f(1)=4 f'(1)=0 从而可以解得a和b X3-3aX2+2bX =X(X2-3aX+2b) =X{(X-3a/2)2+. a=2/3 b=5/