Sum of the angles in an octagon
= (n - 2) × 180° = 6 x 180°= 1080° One angle of the regular octagon
= 1080 – 8 = 135°
One side of the regular octagon = 2 cm.
Radius if the sectors having centre is each vertices of the circle = 1 cm
The second picture shows the cut-down form of 8 sectors having centre angle 135° and radius 1 cm.
The perimeter is found by calculating the length of 8 arc having radius 1 cm and central angle 135°.
Perimeter of the cut down portion
