# How to find the cosine

The cosine of an angle α of a right triangle is defined as the ratio between the adjoining or adjacent leg (b) and the hypotenuse (c).

## Cosine Theorem

Cosine theorem, applications. Exercises. This theorem relates one side of the triangle to the other two and the angle they form.

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## Calculating the Cosine of an Angle

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## Law of Cosines

The law of cosines states: c 2 = a 2 + b 2 - 2 ab cos C . This resembles the Pythagorean theorem except that for the third term and if C is a right angle the third term equals 0 because the cosine of 90° is 0 and you get the Pythagorean theorem.

## Cosine of an Angle

The cosine is equal to the length of the side adjacent to the angle divided by the length of the hypotenuse. The cosine is also equal to the sine of the angle