# Thread: basic trig, re;ated acute angle

1. ## basic trig, re;ated acute angle

Hi I know this is pretty basic but just want to make sure i understand

tanA= -2/6

Find two possible values for the measure of angle A and the related acute angle.

Thanks!

2. I you have the form;

tan(x) = k

Where x is an unknown and k is some fixed constant, then...

x = $tan^{-1}(k)$

If you were to just put this in a calculator, you'll only get one answer. However, as you know, there's an infinite amount of answers, so all you do is add/subtract pi to your answer to get the next/previous answer. So really...

x = $tan^{-1}(k) + pi$ or x = $tan^{-1}(k) - pi$

3. Hi thanks for your reply, but we are not at the point of adding or subtracting pi....in other exa,ples we were shown, teach just subtrected answer from 180?

4. -2/6=-1/3 :-)

A=arctan(-1/3)=-arctan(1/3)=-18.43...*

5. thanks!

6. Originally Posted by Chr2010
Hi thanks for your reply, but we are not at the point of adding or subtracting pi....in other exa,ples we were shown, teach just subtrected answer from 180?
Oh, sorry about that, I was using the unit circle. 180 degrees and pi are the same thing, so just subtract by 180.

7. Originally Posted by Chr2010
Hi thanks for your reply, but we are not at the point of adding or subtracting pi....in other examples we were shown, teach just subtracted answer from 180?

Subtracting from 180° (or $\displaystyle \pi$ radians) works for sine and cosecant, but not for the other trig functions.

On the unit circle, add 180° when solving a tangent or cotangent problem. Subtract from 360° when working with the cosine.

These will give you a 2nd answer on the unit circle.