The method to calculate the instantaneous velocity of each counting point is (△ X1 + △ x2) / 2 △ T. how to calculate the instantaneous velocity of the first point and the last point

The method to calculate the instantaneous velocity of each counting point is (△ X1 + △ x2) / 2 △ T. how to calculate the instantaneous velocity of the first point and the last point

All of mine is gone