Sum/Difference Identities

[kristi5590]

I need help doing problems where you have to find the exact values of sin, cos, or tan. For instance like:
cos alpha=3/5 sin beta=-5/13, 3pi/2<alpha<2pi,pi<beta<3pi/2
in QIV in QIII

you must find the exact value of tan(alpha+beta)

 

[tkhunny]

Draw a couple of Right Triangles

3-4-5
5-12-13

This will help you to find the sine, cosine, and tangent of your alpha and beta.

tan(a+b)

You can expand this with the Sum of Angles formula for tangent.

OR, if you don't remember that one, you can convert it, tan(a+b)
= sin(a+b)/cos(a+b) and use those expansion formulas.