I'm not getting this stuff at all. Finding math help online is quite hard, so I hope you guys can help me.

How do you solve problems like these ones:

$\displaystyle sin(arccos(3/5) + arccos(5/13))$

and

$\displaystyle cos(2arcsin(-2/3))$

How do you find the arccos of something like (3/5) without a calculator?!

I have some more questions, but I'll post them later for sake of clarity.

Thanks Everyone