The math book I have does a pretty terrible job explaining this to me, because I am absolutely stumped as to why I get every question wrong in two sections: finding values of each expression in radians (can often be given in terms of ?) and finding approximate/exact values of the expressions. Here is a problem where I have to find values for each expression in radians: Sin^-1(1/2) The answer is ?/6, but as to how they got this answer I am completely stumped. I don't think I got one problem right in the section that I had to use no calculator on. The next ones are worse though, because even though I can do actual calculation I still get them wrong. The problem is tan(Cos^-1(12/13)) and I am supposed to find the value of the expressions: I did Cos^-1 which is hypotenuse/adjacent: Then took tan, which is x/y, so I would get 13/15, but the answer is 5/12! Anyways, any help would be appreciated.