Why does $\displaystyle \cos x \cos (\pi / 4) -\sin x \sin (\pi/4)$ equal $\displaystyle \frac{1}{\sqrt2}(\cos x - \sin x)$? Thanks in advance.
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Originally Posted by Air Why does $\displaystyle \cos x \cos (\pi / 4) -\sin x \sin (\pi/4)$ equal $\displaystyle \frac{1}{\sqrt2}(\cos x - \sin x)$? Thanks in advance. $\displaystyle \cos (\pi / 4) = \sin (\pi / 4) = \frac{1}{\sqrt{2}}$
what is $\displaystyle \cos \frac{\pi}{4}$ ? and $\displaystyle \sin \frac{\pi}{4}$ Did you notice that this can also be written as $\displaystyle \cos (x +\frac{\pi}{4})$ ? Bobak
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