Question

简单的值域题求函数f(x)＝(根号(x+2) -3)/(x-7)的值域

Answer 1

f(x)＝(√(x+2) -3)/(x-7)

设√(x+2)=t(t属于[0,+无穷),t不等于3)

x=t^2-2

f(t)＝(t-3)/(t^2-9)=1/(t+3)

f(t)属于（0,1/3]