Triangle A to B has a change of +3 in x values, but Triangle B to C has a change of +6 values so each triangle doesn’t have the same changes in x values.
Triangle A to B has a change of +2 in y values, Triangle B to C has a change of +4 values so each triangle doesn’t have same change in values.
Triangle A to B change in y over change in x = 2/3, Triangle B to C change in y over change in x = 4/6, both have decimal values of 0.66. Therefore, each triangles has the same ratio of change in y over change in x.