Current i is flowing in hexagonal coil of side a. The magnetic induction at the center of the coil will be

Field due to finite wire,  BAB=μoi4πx(Sin300+Sin300)=μoi4πx(12+12)=μoi4π3a2=μoi3(2πa)     (∵OA=a , △AOB is equilateral) ∴Total magnetic induction due to all the sides at O, B=6BAB=6μoi23πa=3μoiπa