## cosine (COS)

### Cosine (COS) is one of the trigonometric functions used in mathematics

Cosine (COS) is one of the trigonometric functions used in mathematics. It is defined as the ratio of the length of the adjacent side of a right triangle to the length of the hypotenuse.

In a right triangle, one angle is 90 degrees (a right angle). The cosine of an angle θ, denoted as cos(θ), is calculated by dividing the length of the adjacent side by the length of the hypotenuse. Mathematically, cos(θ) = adjacent/hypotenuse.

The value of cosine ranges from -1 to 1. It is positive in the first and fourth quadrants, where the angle is between 0 and 180 degrees, and negative in the second and third quadrants, where the angle is between 180 and 360 degrees.

Cosine function is widely used in various fields of mathematics and physics, particularly in trigonometry, calculus, and geometry. It helps in solving problems related to angles, distances, and various waveforms such as sound, light, and electromagnetic waves.

It is important to note that cosine is a periodic function, which means that its values repeat in a cyclical manner as the angle increases. The cosine of complementary angles (summing up to 90 degrees) is always equal, but with opposite signs.

In summary, cosine is a trigonometric function used to find the ratio of the length of the adjacent side to the length of the hypotenuse in a right triangle, and it is fundamental in studying angles and waveforms.

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