xx Theory
One final type of power product has a different nature. It is important for the topic of Fourier series (in ODE) so we study it. Here the frequency varies, while the power is always
For example, consider:
This type of integrand may be converted to a sum of single-factor trig functions using these identities, which are created by solving the angle-sum and angle-difference formulas for the desired product:
These should be rederived, when needed, from the sum and difference trig identities.
xx Illustration
Example - Differing frequencies