分离常数法
y=(4x-5)/(5x-3)
=[ (4/5)(5x-3)-13/5 ] /(5x-3)
=4/5- (13/5)/(5x-3)
则于(13/5)/(5x-3)≠0
所以y≠4/5
值域{y| y≠4/5}