（xy-x的平方）÷xy分之x-y
=x(y-x)*xy/(x-y)
=-x^2y
(x的平方+x分之4x的平方-1）乘(1-2x分之x+1)÷x分之1
=[x(x+1)分之(2x+1)(2x-1)]乘(1-2x分之x+1)*x
=-(2x+1)
=-2x-1
x-y分之x+y÷（xy+x的平方）
=(x+y)/(x-y)÷[x(x+y)]
=1/x(x-y)
=1/(x²-xy)
(4x的平方-4x+1分之x)÷2x的平方-x分之1
=[(2x-1)²分之x]*x(2x-1)
=x²/(2x-1)