y=5x-1/4x+2
4xy+2y-5x+1=0
4xy-5x=-2y-1
x(4y-5)=-2y-1
x=-2y-1/(4y-5)
x=2y+1/5-4y
互换y=(2x+1)/(5-4x)
此时定义域为x≠5/4 即为原函数的值域 y≠5/4