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ΔABD, ΔADE, ΔCDE kongruen
Sehingga : 
AB = AE = CE = 12 cm
AC = 24 cm

(BC)² = 24² - 12²
         = 576 - 144
(BC)² = 432
BC = √432
      = √(144.3)
BC = 12√3 cm

Perbandingan :
AB/BC = AD/AC

12/12√3 = AD/24

1/√3 = AD/24

AD√3 = 24

AD = 24/√3

AD = (24√3)/3

AD = 8√3 cm


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