jika panjang busur ab=77/12cm dan sudut AOB=105,maka panjang OA adalah

ab = 105/360 . 2π.r
77/12 = 105/360. 2. 22/7 .r
r= (77.360.7)/(12.105.2.22)
= 3,5 cm

semoga mmbantu

busur AB = 77/12 cm
< AOB = 105°

busur AB = < AOB/360° × 2 × phi × OA
77/12 = 105°/360° × 2 × 22/7 × OA
77/12 = 660/360 × OA
77 × 360 = 12 × 660 × OA
27720 = 7920 × OA
OA = 27720/7920
OA = 3,5 cm

jadi panjang OA adalah 3,5 cm