1. More Simplifying

Hi
I need help on the following questions:
Simplify the following expression in an exact form: $cos(sin^{-1}\frac{4}{5})$

P.S

2. exact form

$\cos\left(\sin^{-1}\left(\frac{4}{5}\right)\right) = \frac{3}{5}$

3. can this be done without using the calculator??

4. you are looking at a 3,4,5 triangle

5. ok ic