tolong bantu soal nomer 3 dan caranya ya, terimakasih semoga ilmu anda bermanfaat

•3

∆ABC

K = AB + BC + CA
K = 25 cm + 20 cm + 15 cm
K = 60 cm

S = ½ K
S = ½ . 60 cm
S = 30 cm

L = √s (s-a) (s-b) (s-c)
L = √30 (30-25) (30-20) (30-15)
L = √30 . 5 . 10 . 15
L = √22500 = 150 cm²

L. ∆ABC = 150 cm²

L. ∆ADC = 150 cm² x 14/25
L. ∆ADC = 84 cm²

L. ∆ADC = CD x CA x ½
84 cm² = CD x 15 cm x ½
84 cm² = CD x 7,5 cm
CD = 84 cm²/7,5 cm
CD = 11,5 cm

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