\cos( \alpha + (\pi)/(2) ) = - \sin( \alpha ) why is it equal

asked Jul 8, 2020 192k views

2 votes

$\cos( \alpha + (\pi)/(2) ) = - \sin( \alpha )$
why is it equal

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3 votes

$\cos (\alpha +(\pi)/(2))= \cos((\pi)/(2))\cos (\alpha)- \sin((\pi)/(2))\sin(\alpha)\\=0-\sin(\alpha)\\=-\sin (\alpha)$

Philipp Munin answered Jul 14, 2020

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