题解 | 三角形面积

#include <bits/stdc++.h>
#include <cmath>
#include <math.h>
using namespace std;

struct point {
    double x, y;
    point(double A, double B) {
        x = A, y = B;
    }
    point() = default;
};

struct triangle {
    point a, b, c;
    triangle(point A, point B, point C) {
        a = A, b = B, c = C;
    }
    triangle() = default;
};

double getArea(triangle T) {
    // TODO: 计算三角形T的面积
    double a = sqrt(pow((T.b.y - T.a.y), 2) + pow((T.b.x - T.a.x), 2));
    double b = sqrt(pow((T.c.y - T.b.y), 2) + pow((T.c.x - T.b.x), 2));
    double c = sqrt(pow((T.a.y - T.c.y), 2) + pow((T.a.x - T.c.x), 2));

    double cosB = (a * a + c * c - b * b) / (2 * a * c);

    double sinB = sqrt(1 - cosB * cosB);
    double minji = (a * c * sinB) / 2;
    return minji;
}






























































































































































































int main() {
    int x, y;
    cin >> x >> y;
    point a(x, y);
    cin >> x >> y;
    point b(x, y);
    cin >> x >> y;
    point c(x, y);
    triangle T(a, b, c);
    cout << fixed << setprecision(2) << getArea(T) << endl;
    return 0;
}