Examine the diagram of the triangle at right.  

1. Write an equation representing the relationship between $x, y,\text{ and }r$.

   Hint (a):

   Think of the Pythagorean Theorem.

2. Write an expression for $\sin\theta$. What is $\sin\theta$ if $r = 1$?

   Hint (b):

   $\text{sin}\theta = \frac{\text{opp}}{\text{hyp}}$

   Answer (b):

   $\sin\theta = \frac{y}{r}\:\:\:\:\:\:\:\:\:\:\:\:\:\: \sin\theta = y$

3. Write an expression for $\cos\theta$. What is $\cos\theta$ if $r = 1$?

   Hint (c):

   $\cos\theta = \frac{\text{adj}}{\text{hyp}}$