public class Droites {
	public static void main(String[] args) {
		droite(1, 1, 2, 2);
		if(appartient(-1,1, 0, 2, 2)){
			System.out.println("yay");
		}
		
	}
	public static void droite(double x1, double y1, double x2, double y2){
		double dir_x = x2 - x1, dir_y = y2 - y1;
		double a = -dir_y, b = dir_x;
		double c = a*x1 + b*y1;
		System.out.println("equation de la droite: " + a + "x + " + b + "y = " + c);
	}

	public static boolean appartient(double a, double b, double c, double x, double y){
		return a * x + b * y == c ;

	}
}