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# question

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what's the difference between cos( and cos-1( ?????

Jan 9, 2019

#1
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cos theta is a ratio, it is always between -1 and +1

inverse cos is an angle.    Inverse cos is the same as arc cos.

In the trianlge illustrated:

$$\boxed{cos \theta = \frac{adj}{hyp}\\~\\ cos^{-1}\left( \frac{adj}{hyp}\right)=\theta\\}\\~\\ also\\~\\ acos\left( \frac{adj}{hyp}\right)=cos^{-1}\left( \frac{adj}{hyp}\right)=\theta\\~\\$$

Jan 9, 2019