中垂线定理

#include
using namespace std;
#define db double
#define ll long long
#define pii pair
#define mm(a,b) memset(a,b,sizeof(a))
#define rush() int T; cin >> T; while (T–)
#define ACCELERATE (ios::sync_with_stdio(false),cin.tie(0))
const int N = 2e5 + 5;
const int M = (N << 2);
struct Point {
db x, y;
Point (db _x = 0, db _y = 0): x(_x), y(_y) {}
void input() { cin >> x >> y; }
};
Point solve(Point a, Point b, Point k)
{
db a1 = b.x - a.x, b1 = b.y - a.y;
db a2 = k.x - a.x, b2 = k.y - a.y;
db c1 = (a.x + b.x) / 2, d1 = (a.y + b.y) / 2;
db c2 = (a.x + k.x) / 2, d2 = (a.y + k.y) / 2;
db t2 = (a1 * (c1 - c2) + b1 * (d1 - d2)) / (b1 * a2 - a1 * b2);
return Point(c2 - t2 * b2, d2 + t2 * a2);
}
int main()
{
ACCELERATE;
Point a, b, k;
a.input();
b.input();
k.input();

Point c = solve(a, b, k);
return 0;

}