The Student Room Group

De Moivre's Theorem

((2cosx)^3)*((2jsinx)^4)=(z+z^-1)^3*(z-z^-1)^4
I have this down in my notes as a way of solving for cos^3xsin^4x.
I understand you can use binomial expansion, then replace certain parts with their respective multiple angle formula. But I remember my teacher mentioning another less cumbersome way of doing it, which I didn't write down :/ Does anyone know what they might have been talking about, or just a different way of doing it?
Thanks in advance.
Original post by Chromatic
((2cosx)^3)*((2jsinx)^4)=(z+z^-1)^3*(z-z^-1)^4
I have this down in my notes as a way of solving for cos^3xsin^4x.
I understand you can use binomial expansion, then replace certain parts with their respective multiple angle formula. But I remember my teacher mentioning another less cumbersome way of doing it, which I didn't write down :/ Does anyone know what they might have been talking about, or just a different way of doing it?
Thanks in advance.


What is there to solve?
Reply 2
Original post by NotNotBatman
What is there to solve?


Probably didn't make it clear enough. I'm not solving, I'm simplifying (z+1/z)^3(z-1/z) ^4 into multiple angle form, ultimately to get equations for cos cubed x and sin ^4 x in terms of multiple angles.

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