Tolong jawab nomor 3 dengan cara

AB (c) = 12 cm
BC (a) =....???
L ABC = 27 cm^2
Sudut ABC (b) = 180°-120°=60°
L ABC = 1/2 × a × c × sin b
27 = 1/2 × a × 12 × sin 60°
27 = 1/2 × a × 12 × 1/2 akar 3
27 = ( 3 akar 3 ) × a
a = 27 / 3 akar 3
a = 3 akar 3
jadi panjang BC = ( 3 akar 3 ) cm