# How To Do Trigonometry For This...?

• Jan 10th 2009, 05:31 PM
AlphaRock
How To Do Trigonometry For This...?
I know how to do cos(5pi/6) and any question like it.

But I don't know how to do sin, cos, tan, csc, cot, sec, of angles like 0 (0pi/12), 90 (3pi/12), 180 (6pi/12), 270 (9pi/12), 360 (12pi/12), 450 (15pi/12), etc.

Can somebody show me how?

ALso, I don't understand why cos (0pi/12) = 0, too. Or why some are undefined.
• Jan 10th 2009, 05:56 PM
skeeter
there is nothing to "do" here ... this is just a matter of knowing the unit circle.

note that $\cos\left(\frac{5\pi}{6}\right) = -\frac{\sqrt{3}}{2}$

http://math.asu.edu/%7Enbrewer/Sprin...nit_circle.gif

here is how to find a trig value for an angle involving $\frac{\pi}{12}$ that is not on the unit circle ...

$\cos\left(\frac{\pi}{12}\right) = \cos\left(\frac{\pi}{3} - \frac{\pi}{4}\right)$

you need the difference identity for cosine to calculate the exact value ...

$\cos(a-b) = \cos(a)\cos(b) + \sin(a)\sin(b)$

If none of this makes sense to you, then it's obvious that you have some major gaps in your knowledge of basic trigonometry. you should see your teacher to get some face to face help.

finally ... "cos(0pi/12)" = cos(0) = 1 , not 0.