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# What is cos() in C?

harris910

The cos() function returns the cosine of a number. To be more specific, it returns the cosine of a number in the radian float value.

Figure 1 shows the mathematical representation of the cos() function.

Figure 1: Mathematical representation of cosine function

Note:

• The math.h header file is required for this function.
• This cos() function only works for right-angled triangles.

## Syntax

double cos(double num)


## Parameter

This function requires a number that represents an angle in radians as a parameter.

In order to convert degrees to radians, use the following formula:

radians = degrees * ( PI / 180.0 )


## Return value

cos() returns the cosine of a number (radians float value) that is sent as a parameter.

## Example

#include<stdio.h>
#include<math.h>

int main() {
printf("The cosine of %lf is %lf \n", 2.3, cos(2.3));

printf("The cosine of %lf is %lf \n", -2.3, cos(-2.3));

//converting the degrees angle into radians and then applying cos()
// degrees = 90.0
// PI = 3.14159265
// result first converts degrees to radians then apply cos
double result=cos(90.0 * (3.14159265 / 180.0));
printf("The cosine of %lf is %lf \n", 90.0, result);

}

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