tolong di jawab dong? besok dikumpulin nih?

∆ABC

CD² = AD × DB
CD² = 4 × 16
CD = √64
CD = 8 cm

BC (dg Pythagora)
BC = √(CD² + BD²)
BC = √320
BC = 8√5 cm

Luas ∆ABC
= 1/2 × AB × CD
= 1/2 × 20 × 8
= 80 cm²