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Why does matlab change cos / sin input?

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Wouter van den Wijngaard
Wouter van den Wijngaard on 17 Feb 2020
Hello,
Something very weird happens when i try to integrate cos / sin functions. Matlab changes te values i put in the cos / sin for example this happens when i want to integrate acceleration (a) to speed (v):
>> syms x
>> a=cos(-2*x+3)
a =
cos(2*x - 3)
How can i avoid this?

  2 Comments

John D'Errico
John D'Errico on 17 Feb 2020
Why does it matter at all? cos(X) == cos(-X). So it changes nothing.
Stephen Cobeldick
Stephen Cobeldick on 17 Feb 2020
"Something very weird happens when i try to integrate cos / sin functions..."
Why is it weird? They are exactly equivalent.

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Answers (1)

Siriniharika Katukam
Siriniharika Katukam on 20 Feb 2020
Hi
Assuming that your issue is the change of signs in the "cos" function, the interpreted value of a as cos(2*x - 3) is right as "cos(x) = cox(-x)". You will get the same values when you try to integrate both cos(-2*x + 3) and cos(2*x – 3).

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