symbolic of cos with power

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student
student 2014-4-7
回答： Karan Gill 2016-12-9
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?

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回答（1 个）

Karan Gill
Karan Gill 2016-12-9
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

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