Given right triangle ABCABC with altitude \overline{BD}BD drawn to hypotenuse ACAC. If AD=4AD=4 and DC=9,DC=9, what is the length of \overline{BD}?BD? (Note: the figure is not drawn to scale.)
AD / BD = BD / DC
AD * DC = BD^2
4 * 9 = BD^2
36 = BD^2
6 = BD