What is the range of f(x)=tan2x+cot2xf(x) = \tan^2 x + \cot^2 xf(x)=tan2x+cot2x?
[1,∞)[1, \infty)[1,∞)
[2,∞)[2, \infty)[2,∞)
[0,∞)[0, \infty)[0,∞)
(0,∞)(0, \infty)(0,∞)