1.3-17:计算三角形面积

#include<iostream>
#include<iomanip>
#include<math.h>
using namespace std;
int main()
{
	float x1,y1,x2,y2,x3,y3;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	double c=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
	double b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
	double a=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
	double p=(a+b+c)/2;
	double s=sqrt(p*(p-a)*(p-b)*(p-c));
	cout<<fixed<<setprecision(2)<<s;
	return 0;
}