A right triangle ABC has its right angle at C. The two legs from C stay perpendicular as you reshape it: drag A to set one leg's length and the triangle's tilt, drag B to set the other leg, and drag C to move the whole figure. M is the midpoint of the hypotenuse AB, and CM is the median from the right angle to the hypotenuse. The theorem: this median is exactly half the hypotenuse, so CM equals AM equals BM equals half of AB — meaning M is the same distance from all three corners. Equal tick marks show the three equal segments, a right-angle mark sits at C, and the segment lengths are shown live. An info button opens a drawer with the explanation.