[(x的平方-3x)分之(x+3)-(x的平方-6x+9)分之(x-1)]÷x分之(x-9)
=[(x+3)/(x^2-3x)-(x-1)/(x^2-6x+9)])]÷[(x-9)/x]
=[(x+3)/x(x-3)-(x-1)/(x-3)^2]*x/(x-9)
=[(x+3)(x-3)-(x-1)*x]/[x(x-3)^2]*x/(x-9)
=(x^2-9-x^2+x)/[x(x-3)^2]*x/(x-9)
=(x-9)/[x(x-3)^2]*x/(x-9)
=1/(x-3)^2
已知a/ 1-b/1=4,求2a-2b+7ab/a-2ab-b的值(
1/a-1/b=4
(b-a)/ab=4
b-a=4ab
(a-2ab-b)/(2a-2b+7ab)
=(-4ab-2ab)/[2(a-b)+7ab]
=-6ab/(-8ab+7ab)
=-6ab/-ab
=6