Sorry for the vague title, but I'm not sure what to call it.

I have a series of questions based on the above figure, but I'm not sure how to look at it. It asks to state the value of certain trigonometric ratios.

First one is , and the answer in the back of the book is . I'm not sure how they got just as I would have thought it to be for sin.

If anyone could help me read the figure/answer one of the questions so I could finish it off, I would greatly appreciate it!