How do I calculate $\displaystyle cos 7\pi/8$ I only know how to find it if it is on the unit circle >_>
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Originally Posted by dorkymichelle How do I calculate $\displaystyle cos 7\pi/8$ I only know how to find it if it is on the unit circle >_> first, note that $\displaystyle \cos\left(\frac{7\pi}{8}\right) < 0$ let $\displaystyle x = \frac{7\pi}{4}$ use the half-angle formula ... $\displaystyle \cos\left(\frac{x}{2}\right) = \pm \sqrt{\frac{1+\cos{x}}{2}}$
Why do you use [tex] x = 7\pi/4? and the half formula? I don't see the "half" part
Hello dorkymichelle Originally Posted by dorkymichelle Why do you use [tex] x = 7\pi/4? and the half formula? I don't see the "half" part $\displaystyle \cos x=\cos\left(\frac{7\pi}{4}\right)=\cos\left(2\pi -\frac{\pi}{4}\right) =\frac{1}{\sqrt2}$ Grandad
Originally Posted by dorkymichelle Why do you use [tex] x = 7\pi/4? and the half formula? I don't see the "half" part $\displaystyle \frac{1}{2} \cdot \frac{7\pi}{4}$ = ?
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