泪目！第一次花了好多变量，肯定有更简洁的方法吧
#include<stdio.h>
#include<math.h>

int main()
{ double a,b,c,d,e,f,g,h,B,C,D,E,F,G,H,I,J,K,M;double L,A;
scanf("%lf %lf %lf %lf %lf %lf",&a,&b,&c,&d,&e,&f);
g=1.0*(d-b)/(c-a);h=1.0*(f-b)/(e-a);
if(g!=h)
{B=pow((c-a),2);C=pow((d-b),2);D=pow((B+C),0.5);
E=pow((e-a),2);F=pow((f-b),2);G=pow((E+F),0.5);
H=pow((e-c),2);I=pow((f-d),2);J=pow((H+I),0.5);

K=(D*D+G*G-J*J)/(2*D*G);M=pow((1-K*K),0.5);

L=D+G+J;
A=0.5*(D*G*M);
printf("L = %.2f, A = %.2f",L,A);
}
else{
printf("Impossible");
}





return 0;
}