> #include<iostream>
> #include<cmath>
> using namespace std;
> int main()
> {
>     freopen("1.txt","w",stdout);
>     int t;
>     scanf("%d",&t);
>     while(t--)
>     {
>         double ax,ay,bx,by,cx,cy;
>         scanf("%lf%lf%lf%lf%lf%lf",&ax,&ay,&bx,&by,&cx,&cy);
>         double hy=(((cx-ax)*(ax-bx)+(ay-by)*cy)*(cx-bx)+(by-cy)*(ax-bx)*ay)/((by-cy)*(ax-bx)+(cx-bx)*(ay-by));
>         double hx;
>         if(abs(ax-bx)>1e-8)hx=cx-(hy-cy)*(ay-by)/(ax-bx);
>         else hx=ax-(ay-hy)*(by-cy)/(cx-bx);
>         printf("%.4lf %.4lf\n",hx,hy);
>     }
>     return 0;
> }
除数会不会为0