y=5x-1／4x+2,求值域

题目

y=5x-1／4x+2,求值域

答案

y=(5x-1)／(4x+2)
=(5x+5/2-7/2)/(4x+2)
=(5x+5/2)/(4x+2)-7/[2(4x+2)]
=5/4-7/(8x+4)
因为7/(8x+4)不等于0,
y=5/4-7/(8x+4)不等于5/4
所以
y=（5x-1）／（4x+2）的值域为y不等于5/4