# I don't undestand these trig angle questions at all.

• Sep 26th 2012, 06:41 AM
ChrisTurner91
I don't undestand these trig angle questions at all.
Find theta, 0 < theta < 2pi, if tan theta= 0.66

Find theta, 0 < (or equal to) theta < (or equal to) 360 if cos theta= -0.89

Am I over-thinking these questions or does it actually have an extensive answer? To me, my guess is for 1, to do .66 tan-1 and for 2, to do -0.89 cos-1, but that seems to simple.
• Sep 26th 2012, 06:59 AM
Plato
Re: I don't undestand these trig angle questions at all.
Quote:

Originally Posted by ChrisTurner91
Find theta, 0 < theta < 2pi, if tan theta= 0.66
Find theta, 0 < (or equal to) theta < (or equal to) 360 if cos theta= -0.89
Am I over-thinking these questions or does it actually have an extensive answer? To me, my guess is for 1, to do .66 tan-1 and for 2, to do -0.89 cos-1, but that seems to simple.

For the first there are two answers: $\displaystyle \arctan(0.66)~\&~\arctan(0.66)+\pi$.

What are the two for the second part?
• Sep 26th 2012, 07:03 AM
ChrisTurner91
Re: I don't undestand these trig angle questions at all.
arccos(-0.89) and arccos(-0.89) + pi?

So I'm just using the inverse function to solve for it?
• Sep 26th 2012, 07:39 AM
Plato
Re: I don't undestand these trig angle questions at all.
Quote:

Originally Posted by ChrisTurner91
arccos(-0.89) and arccos(-0.89) + pi?
So I'm just using the inverse function to solve for it?

No there is far more to it than that.
So you must convert $\displaystyle \arccos(-0.89)$ to degrees.