Trigonometric Power Reduction Formulas using Symbolic Matlab

Hi,

How can i get 1/2(1-cos(2*a)) by rewriting sin(a)^2 using Symbolic Matlab toolbox?

On the other hand if I use rewrite(.5*(1- cos(2*a)),'sin'), i will get sin(a)^2, can't I do the reverse of this process?

Thanks

Answer 1

[Karan Gill]

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

>> syms a
>> f = sin(a)^2;
>> combine(f,'sincos')
ans =
1/2 - cos(2*a)/2

[Star Strider]

Wow! The combine function has been around since R2014a. I need to read the Release Notes more carefully.

Answer 2

[Walter Roberson]

syms a
simplify(rewrite(rewrite(sin(a)^2,'tan'),'sin'))