Section+6.2

=Section 6.2: Sum of Difference Identities= I. Sum and Difference Identities for the Cosine Function - The difference identity for the cosine function is: cos(alpha – beta) + sin(alpha)sin(beta) - Sum and Difference Identities for the Cosine Function: Sum – cos(A + B) = cosAcosB – sinAsinB Difference – cos(A – B) = cosAcosB + sinAsinB

II. Sum and Difference Identities for the Sine Function - Sum and Difference Identities for the Sine Function: Sum – sin(A+B) = sinAcosB + cosAsinB Difference – sin(A-B) = sinAcosB – cosAsinB

III. Sum and Difference Identities for the Tangent Function - Sum and Difference Identities for the Tangent Function Sum – tan(A+B) = tanA + tanB/ 1- tanAtanB Difference – tan(A-B) = tanA – tanB/ 1+tanAtanB

-The sum and difference identities allowed us to evaluate a trigonometric function exactly for any multiple of 15 degrees(i.e., pi/12)