Angles of elevation and depression!

The term "angle of elevation" refers to the angle above the horizontal from the viewer. If you're at point A, and AH is a horizontal line, then the angle of elevation to a point B above the horizon is the angle BAH. Likewise, the "angle of depression" to a point C below the horizon is the angle CAH.
Tangents are frequently used to solve problems involving angles of elevation and depression.


Common angles
We can extend our table of sines and cosines of common angles to tangents. You don't have to remember all this information if you can just remember the ratios of the sides of a 45°-45°-90° triangle and a 30°-60°-90° triangle. The ratios are the values of the trig functions.
Note that the tangent of a right angle is listed as infinity. That's because as the angle grows toward 90°, it's tangent grows without bound. It may be better to say that the tangent of 90° is undefined since, using the circle definition, the ray out from the origin at 90° never meets the tangent line.