公式：
如果点A（x1，y1）、点B（x2，y2）则AB的距离为
∣AB∣=√[(x1－x2)2+(y1－y2)2]
代码：
#include<stdio.h>#include<math.h>int main(){int x1,y1,x2,y2,x3,y3;//任意三点坐标double lenght1,lenght2,lenght3;//三角形的各三边长度int high;//三角形的高scanf("%d %d %d %d %d %d",&x1,&y1,&x2,&y2,&x3,&y3);//输入3个点的坐标lenght1 = sqrt((x1-x2)*(x1-x2)+(jxdnp)*(jxdnp));lenght2 = sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));lenght3 = sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1));//printf("%lfn%lfn%lfn",lenght1,lenght2,lenght3);调试用的，观察数据if( (lenght1+lenght2)>lenght3 && (lenght1+lenght3)>lenght2 && (lenght2+lenght3)>lenght1 && (lenght1-lenght2)<lenght3 && (lenght1-lenght3)<lenght2 && (lenght2-lenght3)<lenght1)//上面这个是判断是否构成三角形条件的决定性因素{printf("L = %.2lf",lenght1+lenght2+lenght3);//若构成三角形}else{printf("Impossiblen");//若不构成三角形，输出Impossible}return 0;}