Finding complex number from polar coordinates

Thanks for all the help on the previous problems, I figured out all my problems! Now, I'm stuck on another kinda simple area. Converting polar coordinates to complex numbers...

Give the complex number whose polar coordinates $\displaystyle (r,\theta)$ are

(a) $\displaystyle (\sqrt{3},\frac{\pi}{4})$

(b) $\displaystyle (4, \frac{-\pi}{2})$

If someone could just walk me through one of the problems, I would greatly appreciate it! I have 6 of these to do, and I'm pretty sure I can figure them all out if someone can provide me with a walk-through on one! Thanks, and good night! zzzz