Question

locate the points - 2, 4 and 3, - 1 and -1, 0 joined the point and get area of triangle​

Answer 1

I will tell you opposite of it that is WHAT IS THE CONDITION OF THREE POINTS SO THAT IT DOESN'T FORM TRIANGLE ?
The three points should not be on straight line you can check it bye adding length of two sides and it should always be greater than the third side, if not then it is not a triangle.
Apart from this at any condition the point are if it follows the above criteria that is sum of two sides greater than third side, then it forms a triangle.