简单求定义域 会的来帮帮忙

f(x)的定义域为[-1,4],
则f(1/x +2)要满足
-1<=1/x+2<=4
-3<=1/x<=2

若-3<=1/x<0
则0<1/(-x)<=3
所以1/[1/(-x)]>=1/3
即-x>=1/3
x<=-1/3

若0<1/x<=2
则x>=1/2

所以定义域(-∞,-1/3]∪[1/2,+∞)

f(x)的定义域为[-1,4],
-1≤1/x+2≤4
-3≤1/x≤2
x≤-1/3,或，x≥1/2
f(1/x +2)定义域:(-∞,-1/3] U [1/2,+∞)

1/x +2∈[-1,4],
∴x∈（-∞，-1/3]∪[1/2，+∞)

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