Cosine of an Angle

A right triangle is shown.  What is cos A?

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Cosine of an angle is the ratio of the adjacent side to the hypotenuse.

  adjacent
------------ = cosine
hypotenuse

Find the side adjacent to ∠A (next to angle A), and find the hypotenuse (side across from the right angle).

                 8
cos A = -----   {adjacent over hypotenuse}
                17

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