perhatika gambar diatas,maka panjangAC pake cara y

AC/AB =CD/DE
CD+AD/9 =CD/6
6CD + 6AD = 9CD
6AD = 9CD - 6CD
6 . 4 = 3 CD
24 = 3CD
CD = 24/3 = 8

AC = AD + CD
      = 4 + 8
      = 12