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Azzera filtri

Can only find one double angle formula of cos(2x).

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close all
clear
clc
syms x
expand (cos(2*x))
ans =
2*cos(x)^2 - 1
That is one of the three double angle formulas for cos(2x).
How do I get matlab to show the other two double angle formulas?

Risposta accettata

Star Strider
Star Strider il 10 Set 2021
Experiment with various options to get at least one more identity —
syms x
f(x) = cos(2*x)
f(x) = 
f1 = expand (f)
f1(x) = 
f2 = rewrite(f, 'exp')
f2(x) = 
f3 = rewrite(f2, 'sin')
f3(x) = 
.
  5 Commenti
Jan
Jan il 10 Set 2021
@John Ooi: He adds:
0 = 1 - 1 = 1 - (sin(x)^2 + cos(x)^2) = ...
= 1 - sin(x)^2 - cos(x)^2
@John D'Errico: Yes, Matlab does not care, because all these expressions are equivalent. But I was curious how to bring the symbolic engine to express the different forms. Thanks for showing this.

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