Okay, let us take the problem axis-by-axis. Points A(4,0) and B(3,7) are the vertices of the right triangle ABC. These points are 1 (4-3) unit away from each other on the x-axis, and 7 (7-0) units away from each other on the y-axis. Now, if we want to know the coordinates of point C, it should lie perpendicular to both points A and B since there must be a right angle at this point. Moreover, pt C must be 7 units under (vertical distance) pt B and 1 unit behind (horizontal distance) pt A, thus C(3,0).