1 Answer

Raddicus · Answer 1 · 2023-05-03T01:52:26+0000

The formula for the sum of angles in cosine is:

$\cos (a+b)=\cos (a)\cdot\cos (b)-\sin (a)\cdot\sin (b)$

So in this case the error is adding instead of substracting.

Let's correct it:

$\cos (x+(3\pi)/(2))=\cos (x)\cos ((3\pi)/(2))-\sin (x)\sin ((3\pi)/(2))$

$\cos (x+(3\pi)/(2))=\cos (x)\cdot0-\sin (x)\cdot-1$

$\cos (x+(3\pi)/(2))=\sin (x)$

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