The value of $${\sin ^{ - 1}}\left( {{3 \over 5}} \right) + {\tan ^{ - 1}}\left( {{1 \over 7}} \right)$$ is equal to

The principal value of $${\sin ^{ - 1}}x$$ lies in the interval

Let x, y, z be positive real numbers such that x, y, z are in GP and $${\tan ^{ - 1}}x$$, $${\tan ^{ - 1}}y$$ and $${\tan ^{ - 1}}z$$ are in AP. Then which one of the following is correct?

What is the value of $$\cos (2{\cos ^{ - 1}}0.8)$$ ?