4

#include <stdio.h>

const int n = 4;
const int m = 3;
int a[n][m] = {
    {7, 5, -40},
    {-5, 4, -6},
    {1, 2, -8},
    {0, 1, -4}
};
//Знаки =, >=, <= в уравнениях (1 -> >=) (0 -> =) (-1 -> <=)
int b[n] = {-1, -1, 1, -1};

double max(double a, double b) {
    return ((a > b) ? a : b);
}

double L(double x, double y) {
    return x + 2 * y;
}

bool intersection(int *f1, int *f2, double *x, double *y) {
    double a = f1[0] * f2[1] - f2[0] * f1[1];
    if (a == 0)
        return false;
    *x = (f2[2] * f1[1] - f1[2] * f2[1]) / a;
    *y = (f2[0] * f1[2] - f1[0] * f2[2]) / a;
    return true;
}

bool check_condition(double x, double y) {
    bool result = true;
    for (int i = 0; i < n; ++ i) {
        double v = a[i][0] * x + a[i][1] * y + a[i][2];
        if (b[i] == 0)
            result &= (v == 0);
        else
            result &= (v * b[i] >= 0);
    }
    return result;
}

int main(void) {
    bool iswrite = false;
    double mx, xmx, ymx;
    for (int i = 0; i < n; ++ i) {
        for (int j = 0; j < n; ++ j) {
            if (i == j) continue;
            double x, y;
            if (intersection(a[i], a[j], &x, &y) && check_condition(x, y)) {
                //printf("! %f %d %d\n", L(x, y), i, j);
                if (!iswrite) {
                    mx = L(x, y);
                    xmx = x;
                    ymx = y;
                    iswrite = true;
                }
                else {
                    double f = L(x, y);
                    if (f > mx) {
                        mx = f;
                        xmx = x;
                        ymx = y;
                    }

                }
            }
        }
    }
    printf("%f -> (%f, %f)\n", mx, xmx, ymx);
    return 0;
}