10-3

10-3 is on Half angles and double angles.
There are a lot of formulas in this section.

Half angle formulas:

• sin(a/2)=+/-square root of (1-cosa)/2
• cos(a/2)=+/-square root of (1+cosa)/2
• tan(a/2)=1-cosa/sina
• tan(a/2)=sina/1+cosa

Double angle formulas:

• sin2a=2sinacosa
• cos2a=cos^2-sin^2a
• cos2a=2cos^2a-1
• cos2a=1-2sin^2a
• tan2a=2tana/1-tan^2a

Ex. 1: 2sin20cos20

1. The first thing you would do for this is replace this problem with the formula it equals to.
2. So the formula you would replace it with is sin2a.
3. So that would give you sin2(20)=sin40 degrees
   

Ex. 2: 2tan60/1-tan^260

1. Just like the example above ^^^^, you would replace this problem with the formula it equals to.
2. The formula you would replace it with tan2a.
3. That would give you tan2(60)=tan120 degrees.

That's pretty much it for this section.
-Amber :)