沒指明用什麼語言， 用C寫了。

#include

#include

int main(){

double x1, y1, x2, y2, x3, y3;

double k, b, t;

//輸入3個座標:

printf("Input point A:x, y:");

scanf("%lf, %lf", &x1, &y1);

printf("Input point b:x, y:");

scanf("%lf, %lf", &x2, &y2);

printf("Input point C:x, y:");

scanf("%lf, %lf", &x3, &y3);

k = (y2-y1)/(x2-x1);

b = y1-k*x1;

t = k*x3 + b;

if (fabs(y3-t)

printf("三點在一條直線上。\n");

else

printf("三點不在一條直線上。\n");

return 0;

}