# Thread: Find the trigonometric values of theta.

1. ## Find the trigonometric values of theta.

My teacher wasn't very thorough with the lesson and I'm pretty lost on how to go about doing this.

Basically I have to find all of the trigonometric values of the following:

$\displaystyle \tan \theta = -4 , \sin \theta > 0$

What steps do I need to take in order to find sin, cos, tan, csc, sec, and cot using the following information?

2. Hello, dagbayani481!

$\displaystyle \tan \theta = \text{-}4 ,\;\;\sin \theta > 0$

$\displaystyle \text}Find all of the trignometric values of }\theta.$

We know that tangent is negative in quadrants 2 and 4.
We know that sine is positive in quadrants 1 and 2.
. . Hence, $\displaystyle \,\theta$ is in quadrant 2.

Code:
          *
\
\
\ @
- - - - * - - -

We know that: .$\displaystyle \tan\theta \:=\:-\dfrac{4}{1} \:=\:\dfrac{opp}{adj}$

So the diagram looks like this:

Code:
          *
|\
4 | \
|  \ @
- - * - * - - -
-1

We have: .$\displaystyle opp = 4,\;adj = \text{-}1$

Pythagorus says: .$\displaystyle hyp \:=\:\sqrt{4^2 + (\text{-}1)^2} \:=\:\sqrt{17}$

Now you can write all six trigonometric values.

3. Thanks that really helped!

I tried working it out myself before I saw the answer. I got something similar except instead of having the opp. side as 4 and the adj. side as -1, I had the opp. side as -4 and the adj. side as 1. Does it make a difference where you chose to put the negative?

4. Originally Posted by dagbayani481
Does it make a difference where you chose to put the negative?
It does as that would put this triangle in either the 3rd or 4th quadrant.

But in this case you could get away with it as it would not change the result.

5. Yes, it does change the result. If you take "opposite side" as -4 and "near side" as +1, you get the sine, "opposite over hypotenuse" negative when the probelem specifically says it is positive. You would have the wrong signs for sine, cosine, secant, and cosecant.