Perhatikan segitiga BDC, jika diketahui BC = 20cm . tentukan panjang CD

∆ABC samasisi
A = B = C = 60°

CD tegaklurus AB

sin B = CD/BC

CD = BC sin 60°
CD = 4 . 1/2 √3
CD = 2√3 satuan

cara lain :

DB = AB/2 = 4/2 = 2 satuan

BC² = DB² + CD²
CD² = BC² - DB²
CD² = 4² - 2²
CD² = 16 - 4
CD² = 12
CD = √12
CD = √4 . √3
CD = 2√3 satuan