- Certain angle pairs are given special names based on their relative position to one another or based on the sum of their respective measures.
- If two angles are subtracted then they are called Compound angles.
- (A-B) are compound angles because two angles are subtracted.
- cos(A-B) = cosAcoB + sinAsinB RHS expanded
- It should be known both ways.

- cosA – B = cosAcosB + sinAsinB
- cosA + B =cosAcosB – sinAsinB
- sinA – B = sinAcosB – cosAsinB
- sinA + B = sinAcosB + cosAsinB

- These are the 4 compound identities that will be studied
- all the angles in orange are compounded angles.
- On the RHS are the expanded compound angles
- It should be known in both ways (LHS and RHS)

**Why Compound angles?**

- e.g. sin75º determine the value of sin75º without using a calculator
- 75º is not a special angle so we have a
**PROBLEM**. - For a calculator not to be used we will need special angles .
- 75* is an angle between 0* and 90* so special angles can be used.

**instructions**

Double angles

What is the need of double angles? Lets look at an example where the double angles come into play.

**Example**

Simplify to a single tig ratio without the use of a calculator.

** **

** **

Login

Accessing this course requires a login. Please enter your credentials below!