C :

#include<stdio.h>
#include<math.h>
int main()
{
	int t,flagx,flagy;
	double x1,x2,y1,y2,xq,yq;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
		flagy=x2>x1?1:-1;
		flagx=y2>y1?-1:1;
		xq=(x1+x2)/2;
		yq=(y1+y2)/2;
		xq+=flagx*sqrt(3)*fabs(y2-y1)/2;
		yq+=flagy*sqrt(3)*fabs(x2-x1)/2;
		printf("(%.2f,%.2f)\n",xq,yq);
	}
}

C++ :

#include<stdio.h>
#include<math.h>
int main()
{
	int t;
	scanf("%d",&t);
	while(t--)
	{
		double x1,x2,y1,y2,x3,y3,x,y;
		scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
		x=x2-x1;
		y=y2-y1;
		x3=x/2-y*sqrt(3)/2+x1;
		y3=y/2+x*sqrt(3)/2+y1;
		printf("(%.2f,%.2f)\n",x3,y3);
	}
	return 0;
}