The function **double cos(double x);** returns the cosine of x, expressed in radians.

## Function prototype of cos

*double cos(double x);***x**: A floating point value representing an angle in radians.

## Return value of cos

It returns the cosine of x.

## C program using cos function

The following program shows the use of cos function to calculate cosine of an angle.

#include <stdio.h> #include <math.h> #define PI 3.14159 int main(){ double value, radian, degree; printf("Enter an angle in degree\n"); scanf("%lf", °ree); /* * Degree to radian conversion * One radian is equal to 180/PI degrees. */ radian = degree * (PI/180.0); value = cos(radian); printf("The cosine of %lf is %0.4lf\n", degree, value); return 0; }

Output

Enter an angle in degree 45 The cosine of 45.0000 is 0.7071

Enter an angle in degree 180 The cosine of 180.0000 is -1.0000