Question
(b) Rajah 4(b) menunjukkan seutas dawai yang berbentuk bulatan dengan jejari 9cm dibengkokkan untuk membentuk sebuah sektor AOB dengan pusat O dan berjejari 12cm.
Cari sudut bagi sektor AOB dalam radian. [guna \pi = 3.142] [3 markah]
Answer
Hi Farhaini,
For this question, initially, the wire is in a circular shape as shown in the left diagram, then it is reshaped to form the arc on the right. This means that the perimeter of the circle = the perimeter of the sector.
We know that the perimeter of the circle is 2\pi r, and the perimeter of sector is 2r+r\theta, where r\theta is the length of the arc. So we equate these two to find \theta, which is the angle of sector AOB.
Hope this helps! 
1 Like
Ohhh I see Thank you very muchh ! 