>>963
検索してやってみたがあってるか不明
#include <stdio.h>
#include <math.h>
#define PI 3.1415921356
#define E 0.000001 // 収束半径？
int main()
{
    double A,B,C;
    const double MIN = -PI/2;　const double MAX = PI/2;
    double a,x;　double fx,fdx;
    printf("A,B,C?:");
    scanf("%lf,%lf,%lf",&A,&B,&C);
    // f(X) = Bcos(X/2+C)+tan(A) f'(X) = Bcos(X/2+C)-BXsin(X/2+C)/2
    a = MIN;
    while(a < MAX) {
        fx = B*cos(a/2+C)+tan(A);
        fdx = B*cos(a/2+C) - B*sin(a/2+C)/2;
        x = a - fx/fdx;
        if(fabs(x - a) < E) {
            a = x;
            break;
        } else {
            a = x;
        }
    }

    printf("解:%lf",a);

    return 0;
}
エクセル持ってないから試せないorz