To calculate the length of the arc, we need to know what fraction of the circle is shown. To do this, we use the angle and compare it with 360˚. This angle is 144°. That is \(\frac{{144^\circ ...

In order to derive the formula to calculate the angle at the centre of the sector, the formulae for the arc length and area of a sector can be rearranged so that we can calculate the fraction of ...