Well, you know SOHCAHTOA, right? The tangent of an angle in a triangle is the length of the opposite side divided by the length of the adjacent side.

Just using that and these two triangles (and radian conversions), you can

**figure out** all the values in the table below. You

**don't need to memorize** the table. Just know SOHCAHTOA and the triangles well.

[IMG]http://uk.wrs.yahoo.com/_ylt=A0WTf2xErLxLXm8AU5FWBQx./SIG=12n8ilud8/EXP=1270742468/**http%3a//www.ltu.edu/courses/lowry/techmath/class/images/u4obj313.gif[/IMG]

Now, do you see how they got that angle? $\displaystyle \tan^{-1}(-1)=\frac{\pi}{4}$. Using the unit circle, you can figure out that [tex]tan^{-1}(-1)=-\frac{\pi}{4}.

Hope that helps

Feel free to ask for more help

Mathemagister