cosine_theorem.c

/*

    cosine_theorem.c

    Law of cosines

https://www.facebook.com/photo/?fbid=2876673779320015&set=gm.1827487697410072

    c^2 = a^2 + b^2 + 2 * a * b * cos(C)

    c  = sqrt( a^2 + b^2 + 2 * a * b * cos(C) )


    C Library  <math.h>
https://www.tutorialspoint.com/c_standard_library/math_h.htm
https://www.programiz.com/c-programming/library-function/math.h
https://en.wikipedia.org/wiki/C_mathematical_functions
https://www.geeksforgeeks.org/c-library-math-h-functions/
https://en.wikibooks.org/wiki/C_Programming/math.h

In C Pi is defined in math.h:
#define M_PI 3.14159265358979323846

https://www.tutorialspoint.com/c_standard_library/c_function_cos.htm
https://www.tutorialspoint.com/c_standard_library/c_function_sqrt.htm
https://www.tutorialspoint.com/c_standard_library/c_function_pow.htm


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

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

//#define PI 3.14159265

int main(void)
{
    double a=3.0, b=4.0, c, gamma_deg, gamma_rad;   // gamma is the angle between the sides a and b

    gamma_deg = 90.0;                               // gamma in degrees

    gamma_rad = (M_PI / 180) * gamma_deg;           // gamma in radians
    //gamma_deg = (180 / M_PI) * gamma_deg;         // gamma in degrees

    c  = sqrt( pow(a,2) + pow(b,2) + 2 * a * b * cos(gamma_rad) );

    printf("\n a = %f \n", a );
    printf("\n b = %f \n", b );

    printf("\n gamma_deg = %f degrees \n", gamma_deg );
    printf("\n gamma_rad = %f radians \n", gamma_rad );

    printf("\n c = %f \n", c );

    printf("\n M_PI = %.16f \n", M_PI );


    return 0;

} // main()