1.) Yes, assuming that you are supposed to simplify that expression, I'm also arriving at .
2.) Hmm, I think there's some information missing here. In order to evaluate , you could use the identity . Since you have the value of , can be found using - but that gives two values for , one positive and another negative. Usually, these type of questions will give a rage for the value of x, or make a comment such as "x is an acute angle", so that you can determine whether is positive or negative.
3.) Please be clearer. Specifically, makes literally no sense.