x(0度,180度]
y(负无穷,0]
令cosx=a
-1<=a<1
(a+1)/(a-1)=[(a-1)+2]/(a-1)=1+2/(a-1)
a=-1,y=0
a趋近于1,y负无穷
y=(cosx+1)/(cosx-1)的定义域和值域是多少?
x(0度,180度]
y(负无穷,0]
令cosx=a
-1<=a<1
(a+1)/(a-1)=[(a-1)+2]/(a-1)=1+2/(a-1)
a=-1,y=0
a趋近于1,y负无穷