(d)πr‌2= 3 π⇒ r = 3 cm ∴ DE = 2r‌2 − 2r‌2cos120° DE = 3r‌2 (∵√3= r)
But AB = 2DE (By similarly of triangles) ∴ AB =2(3r2)=6×(√3)2=18‌cm (∴D and E are the mid-points of OA and OB) ∴ Perimeter of triangle ABC = 3 × 18 = 54 cm