Sum and Difference Links

There are several resources to view proofs of the angle addition and angle subtraction identities.  Look them over and make sure you understand them.  You will be required to prove some of the basic identities on your test and the proofs of these identities require diagrams which may not occur to you during a test situation if you haven’t thought about them before.

Demana Precalculus 5.3 page 421 (a distance formula based proof)

Brown Advanced Math 10.1 p.369 (a law of cosines based proof)

Mr. Richardson’s PowerPoint presentation

            download here

Another website with very elegant triangle proofs:

            http://www.cut-the-knot.org/triangle/SinCosFormula.shtml  and

            http://www.cut-the-knot.org/triangle/SinCosFormula2.shtml (beautiful!)