Deriving Sum and Difference Identities
cos(A + B): Derives the Cosine of the Sum of two angles which is used to find the other sum and difference identitites
http://www.youtube.com/watch?v=ObaA-rYHO9o
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
Deriving Double Angle and Half Angle Identities
cos(2A), sin(2A), tan(2A): This video derives the double angle identities for cosine, sine, and tangent, and provides examples using the formulas.
Half Angle Identities for cosine, sine, and tangent: http://www.youtube.com/watch?v=S9XkwZ4n3b4