y=(ax+b)/(cx+d)值域

题目

y=(ax+b)/(cx+d)值域

答案

首先不能全为0,否则y无意义正.
(1) a = 0,b = 0 (但c,d不均为0),y = 0
(2) a = 0,b ≠ 0,c = 0,d ≠ 0,y = b/d
(3) a = 0,b ≠ 0,c ≠ 0
y = b/(cx + d) = (b/c)/(x + d/c)
此由y = (b/c)/x向左平移d/c得到,值域为y ≠ 0
(4) a ≠ 0,c ≠ 0,b = 0,d≠ 0
y = a/c - (d/c)/(x + d/a)
此由y = -(d/c)/x向上平移a/c,向左平移d/a得到,值域为y ≠ a/c
(5) a ≠ 0,c ≠ 0,b ≠ 0,d = 0
y = a/c + (b/c)/x
此由y = (b/c)/x向上平移a/c得到,值域为y ≠ a/c
(6)a,b,c,d均不为0
y = a/c + [(bc-ad)/c²]/(x + d/c)
此由y = [(bc-ad)/c²]/x向上平移a/c,向左平移d/c得到,值域为y ≠ a/c