# Is cosh and COS same?

Cosh and COS are not the same. They represent different mathematical functions, although they are related in a way.

COSH:
The hyperbolic cosine function, cosh, is a mathematical function that is used to calculate the values of the hyperbolic cosine of a given angle or value. It is defined as the ratio of the adjacent side to the hypotenuse in a right-angled hyperbolic triangle. The hyperbolic cosine function is commonly used in various branches of mathematics, such as calculus and differential equations, as well as in physics and engineering.

COS:
On the other hand, the cosine function, COS, is a trigonometric function that is used to calculate the values of the cosine of a given angle or value. It is defined as the ratio of the adjacent side to the hypotenuse in a right-angled triangle. The cosine function is widely used in geometry, trigonometry, and various other fields of mathematics and physics.

The Relationship between cosh and COS:
Although cosh and COS represent different functions, there is an interesting relationship between them. It is given by the formula cos(z) = cosh(iz), where z is any complex number.

To understand this relationship, let’s break it down:

– cos(z): This represents the cosine function applied to the complex number z. It gives the value of the cosine of z.

– cosh(iz): This represents the hyperbolic cosine function applied to the complex number iz. It gives the value of the hyperbolic cosine of iz.

Now, let’s consider the complex number iz. In the complex plane, iz represents a point that is obtained by rotating the point z by 90 degrees counterclockwise. This rotation can be visualized by multiplying z by the imaginary unit i.

By applying the hyperbolic cosine function to iz, we are essentially calculating the ratio of the adjacent side to the hypotenuse in a right-angled hyperbolic triangle formed by the point iz. This is similar to what the cosine function does for a right-angled triangle in the case of cos(z).

Therefore, the formula cos(z) = cosh(iz) holds true because the complex number iz and its corresponding hyperbolic cosine value represent a rotated version of the complex number z and its cosine value.

This relationship between cosh and COS has various applications in mathematics, particularly in complex analysis and the study of trigonometric and hyperbolic functions.

Cosh and COS are not the same functions, but they are related through the formula cos(z) = cosh(iz), which holds true for any complex number z.