Cosine of the Difference of Two Angles
- Brian Sterr
Cosine of the Sum/Difference of Two Angles
Why is ?
Use the coordinates of and the distance formula to rewrite this equation. Square both sides. Expand everything and simplify. Finally solve for .
Angle Difference Formula for Cosine
Now apply this formula using the angles and . Use even and odd properties to simplify so everything is expressed in terms of functions of and .