# Trig question -sin pi/4 , give the exact value?

1. Jul 11, 2011

### Neopets

1. The problem statement, all variables and given/known data

-sin pi/4 , give the exact value?
-1/root 2 is the answer according to the book? How in the world do they get that result. What do you to make that happen?

2. Relevant equations

3. The attempt at a solution

Also, is this how to do the problem? Find pi/4 on the unit circle, it's root 2 / 2, that doesn't seem to get the right answer even though that's was supposed to be the method?

2. Jul 11, 2011

### QuarkCharmer

$\frac{1}{\sqrt{2}}$ is the same as $\frac{\sqrt{2}}{2}$, simply "rationalize" it by multiplying the top and bottom by $\sqrt{2}$

Basically you have the right idea, you can think of sin as the y-coordinate.
Remember, the problem is "negative" sin pi/4.

3. Jul 11, 2011

### bacon

4. Jul 12, 2011

### 2milehi

It is sloppy to leave a radical in the denominator.

5. Jul 12, 2011

### Mentallic

Not in all cases :tongue:
I don't think the teacher would worry so much about it when it comes to trig.