1. ## Trigonometry

Given that $sin20° = k$, express $tan(-20°)$ in terms of $k$.
I do not really understand this chapter and I was stumped at this question.
Any help and explanation would be greatly appreciated because my teacher has been changed to a trainee from the education institute and I don't get what she's saying half the time.
Thank you very much in advance!

2. $\sin 20 = k$

use the identity $\sin ^2 x + \cos ^2 x = 1$

$\cos 20^o = \sqrt{1 - k^2 }$

so $\tan 20^o = \frac{\sin 20^o }{\cos 20^o }$

$\tan 20^o = \frac{k}{\sqrt{1- k^2}}$

3. Notice that the problem is not yet finished, caramelcake. You asked for tan(-20) and Amer gave you tan(20). Of course, it is easy to finish now.

4. Sorry to nitpick, Amer, but you forgot the degree signs. If I see this:
$\sin 20$
I'm going to assume that you mean 20 radians, not 20 degrees.

This is a pet peeve of mine. I see kids doing this all the time, and it drives me nuts.

5. Originally Posted by eumyang
Sorry to nitpick, Amer, but you forgot the degree signs. If I see this:
$\sin 20$
I'm going to assume that you mean 20 radians, not 20 degrees.

This is a pet peeve of mine. I see kids doing this all the time, and it drives me nuts.
what about now is it ok

6. You should have posted this in the trigonometry section where others may benefit.