tolong jawab no 1 beserta caranya

Diketahui :
Luas juring AOB = 6 cm^2
Jari jari OA = 4 cm
Ditanya : panjang busur AB?
Jawab :

Luas Juring AOB = α/360º x π r2
6 = α/360 × π × 4^2
6 = (16 α/360) π
α = 135 π


Panjang busur AB
= Besar Sudut Juring x 2πr / 360°
= 135 π × 2π4 /360
= 135 × 8 π^2 /360
= 3 π^2 cm