By Pythagoras Theorem
BD^2 + AD^2 = AB ^2
i.e. BD^2 + 3^2 = AB ^2.......(1)

BD^2 + CD^2 = BC^2
i.e BD^2 + 15^2 = BC^2.........(2)

AB^2 + BC^2 = AC^2= 18^2....(3)

Replacing the value of AB^2 and BC ^2 in (3) we get

2BD^2 + 9 + 225 = 324
2BD^2 = 90
BD^2 =45
BD = sr rt of 45= 3*sq rt of 5
=> BD = 6.7(approx)

Answered by Rishoo Singh at 7:54 PM on June 30, 2008