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 $\displaystyle Sin \theta$, and the answer in the back of the book is $\displaystyle b$. I'm not sure how they got just $\displaystyle b$ as I would have thought it to be $\displaystyle \displaystyle \frac{y}{r}$ 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!