You mean, you have the cosine, and want the angle? That is called arc-cosine, often written as cos-1x. Your scientific calculator should have a "shift" key or something similar, which you press, followed by the cosine key. That will give you the inverse cosine or arc-cosine.
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use the SohCahToa method
For a right angle triangle:- hypotenuse = adjacent/cosine or hypotenuse = opposite/sine
Sides have lenght, angles do not. Cosine is the ratio of the adjacent side to the hypotenuse. Cosine can be used to find either of these sides if the other is known.
The cosine function is mathematical equation to determine the adjacent angle of a triangle. The cosine of an angle is the ratio of the length of the hypotenuse: so called because it is the sine of the co-angle.
In a right triangle, the cosine of an angle is defined as the ratio of the adjacent side of that angle to the hypotenuse.