Question

数学分式

b的平方-2b+1分之a-ab

9(y-2x)的立方（x-y)分之12（2x-y)的平方（y-x)

当x=3，y=7时，求分式(xy+2y)-(x+2)分之x的平方-4的值

Answer 1

b的平方-2b+1分之a-ab=(a-ab)/[b^2-2b+1]=a(1-b)/(b-1)^2=a/(1-b)
9(y-2x)的立方（x-y)分之12（2x-y)的平方（y-x)=12(2x-y)^2(y-x)/[9(y-2x)^2(x-y)]
=-4(2x-y)^2(x-y)/[3(2x-y)^2(x-y)]
=-4/3
(xy+2y)-(x+2)分之x的平方-4
=(xy+2y)-(x^2-4)/(x+2)
=(xy+2y)-(x-2)(x+2)/(x+2)
=y(x+2)-(x-2)
x=3,y=7
y(x+2)-(x-2)
=7*5-1
=34