程序代码：

#include <iostream>
#include <format>
#include <cmath>
#include <numbers>
using namespace std;

int main( void )
{
    const double a = 300;
    const double b = 300;
    const double c = 300;

    double mag = sqrt( a*a + b*b + c*c - a*b - b*c -c*a );
    double angle = atan2( (b-c)*std::numbers::sqrt3, 2*a-b-c ) / std::numbers::pi * 180;

    cout << format("magnitude={}, angle={}", mag, angle) << endl;
}