# Nested trig

Calculus Level pending

Let $$f\left( x \right) \equiv \arcsin { (\cos { x } ) }$$ where $$x$$ is measured in radians and $$0<x<\pi$$

What is the value of the following expression?

$$\left| f^{ \prime }\left( \frac { 2\pi }{ 13 } \right) \right|$$

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