3.4

cos(A - B), sin(A + B), sin(A - B): Uses the formula for the cosine of the sum of two angles to derive the formulas for the cosine of the difference of two angles, the sine of the sum of two angles, and the sine of the difference of two angles.  Examples using the formula are provided: http://www.youtube.com/watch?v=B9nWZWIN8_I

tan(A + B): This video derives the identity for the tangent of the sum of two angles: http://youtu.be/AETGkORbNUw

Example 1 finding the tangent of the sum of 2 angles: http://youtu.be/VeHt67oVKPk

Example 2 finding the tangent of the sum of 2 angles: http://youtu.be/NCNN-fShjwc

Example 3 finding the tangent of the sum of 2 angles: http://youtu.be/fBQs8VVuBBM

tan(A - B): This video derives the identity for the tangent of the sum of two angles: http://youtu.be/vjOocEWsXb4

Example 1 finding the tangent of the difference of 2 angles: http://youtu.be/xDzyQWac1Ug

Example 2 finding the tangent of the difference of 2 angles: http://youtu.be/N4PaegaWj5o

Prove Trig Identity 7: http://youtu.be/PIhkiH8-3ds

We verify a Trig identity by using the basic identities and the identity for the sine of a sum or difference.  We prove: (sin(x+y))/(sinx·cosy) = 1 + cotx·tany

Prove Trig Identity 8: http://youtu.be/Hyuave3UzYY

We verify a Trig identity by using the basic identities and the identity for the cosine and sine of a sum or difference.  We prove: (cos(A+B))/(sin(A - B)) = (1 - tanAtanB)/(tanA - tanB)