arctan√(x^2-1)=arccos(1/x)
tan(arctan√(x^2-1))=tan(arccos(1/x))
√(x^2-1)=sin(arccos(1/x))/(1/x)
(1/x)√(x^2-1)=sin(arccos(1/x))
(x^2-1)/x^2=(sin(arccos(1/x)))^2=1-(cos(arccos(1/x)))^2=1-(1/x)^2
x^2-1=x^2-1
上式对任何x都成立
但看原始的式子,
显然,x^2-1>0,x不等于0
即x>1,x1,及0