panjang cd = a.12✓39 b.4✓39 c.3✓39 d.4✓13 e.2✓39

pertama cari dulu panjang BD pake aturan cosinus.

BD = akar(AB^2 + AD^2 - 2 AB AD cos60)
BD = akar(12^2 + 16^2 - 192)
BD = akar(208) = 4 akar(13)

lalu bisa di cari panjang DC, dimana

tan 60 = DC/BD
akar(3) = DC/ 4 akar(13)

DC = akar(3) x 4 akar(13)
DC = 4 akar(39)