in BCD triangle :
DC^2 = BC^2 + BD^2
13^2 = 12^2 + BD^2
169 = 144 + BD^2
BD^2 = 169 - 144
BD^2 = 25
BD = 5
_______________________
In the other hand we have :
BD^2 = AB × BC
5^2 = AB × 12
AB = 25/12
________________________
Also we have :
AD^2 = AB × AC
AD^2 = 25/12 × ( 25/12 + 12 )
AD^2 = 25/12 × ( 25/12 + 144/12 )
AD^2 = 25/12 × 169/12
AD^2 = 25 × 169 / 12 × 12
AD^2 = 5 × 5 × 13 × 13 / 12 × 12
AD = 5 × 13 / 12
AD = 65 / 12
AD = 5.42
Thus the correct answer is option C