I'm not quite sure how to tackle this question. It asks;

a) Find the value of x such that $\displaystyle sin^{-1}x = cos^{-1}x$.

b) On the same diagram, sketch the graphs of $\displaystyle y = sin^{-1}x$, $\displaystyle y = cos^{-1}x$ and $\displaystyle y = sin^{-1}x + cos^{-1}x$.

With this second part, I'm able to sketch the graphs of $\displaystyle y = sin^{-1}x$ and $\displaystyle y = cos^{-1}x$, but I'm not sure how to sketch the third...