Find the derivative of f(x)=sec−1(x)f(x) = \sec^{-1}(x)f(x)=sec−1(x) for ∣x∣>1|x| > 1∣x∣>1.
1/(x^2-1)
1/(|x|\sqrt{x^2-1})
1/\sqrt{1-x^2}
1/(x\sqrt{1-x^2})