If $\frac{1}{2}<|x|<1$, then which of the following is not defined?

$\sin^{-1}x$ $\tan^{-1}x$ $\sec^{-1}x$ $\cos^{-1}x$

$\sec^{-1}x$

$\frac{1}{2}<|x|<1⇒x∈(-1,\frac{-1}{2})∪(\frac{1}{2},1)⇒\sin^{-1}x,\tan^{-1}x,\cos^{-1}x$ are defined and real while $\sec^{-1}x$ is not defined.