兩點距離 sqrt[(x1-x2)(x1-x2)+(y1-y2)(y1-y2)]
#include <math.h>
main(){
clrscr();
printf("頂點為 (1.5,2)(3,1)(2.1,4)的三角形\n");
printf("重心坐標為(%4.1f,%4.1f)\n",(1.5+3+2.1)/3,(2+1+4)/3);
printf("三邊長為%5.3f %5.3f %5.3f \n",sqrt((1.5-3)*(1.5-3)+(2-1)*(2-1)),
sqrt((1.5-2.1)*(1.5-2.1)+(2-4)*(2-4)), sqrt((2.1-3)*(2.1-3)+(4-1)*(4-1)),);
}