Learning Resources

Investigation 7A: Is the Calculator Defective? & Investigation 7B: The Distance Formula and Compound Angle Identities

Step F

Equating the corresponding elements of the two matrices that represent the rotated coordinates, should establish the following:

cos(a + b) = cosa cosb - sina sinb 

sin(a + b) = sinb cosa + sina cosb

These formulas are known as the compound angle identities.