Triangle AEC & FED are similar:
F & D being the middle of AE & CE, ==> FD IS // AC &
Angle EAC =EFD (CORRESPONDING ANGLE & SAME FOR ECA=EDF,
Hence we can write propriety of similar triangle:
CE/CD = AC/FD (CE = 30 & CD=ED =15 & FD = 17)
Then 30/15 = AC/17 ==> AC=34
