Refer to the figure to complete the proportion. a/c=h/? c y b x

The ratio a/c is a comparison of the shorter leg of the right triangle abc to the hypotenuse of the right triangle abc. We notice that h is the shorter leg of the similar right triangle hxb, so we need to compare it to the hypotenuse of the triangle, which in this case would be b.

The full ration then would be a/c = h/b.