B
| D
|
A_______________C
t.h. : AD^2 = BD•DC
BD+DC=BC
BD+DC=5BD
DC=4BD =>DC-4BD=0
BD•DC=576 =>BD=576/DC
DC - 4•576/DC = 0
DC^2 - 2304 =0
DC^2 = 2304 =>DC=48 =>BD=12 =>BC=60
