symbolic of cos with power

I have a long equation with cosine with powers (e.g., (cos(a))^3, (cos(a))^5, ..). Then I need to reduce each power of cosine to unity (but angle is higher): e.g., (cos(a))^2 -> (1+cos(2a))/2.

Here are more examples which reduce various powers:

http://www.proofwiki.org/wiki/Power_Reduction_Formulas

Anyone who knows how to reduce my cosines to unity of power of cosine, using symbolic of matlab?

[MSleiman]

I had a similar question: http://www.mathworks.com/matlabcentral/answers/315371-trigonometric-power-reduction-formulas-using-symbolic-matlab

Answer 1

[Karan Gill]

Here, you want to change the input of "cos" from "x" to "2*x". Essentially, you want make the argument of "cos" more complicated. The "combine" command does that.

syms x
f = cos(x)^2;
combine(f,'sincos')

ans =
cos(2*x)/2 + 1/2