Each fly walks with a velocity v always towards the fliy at its right: always
. Side of the square is 2a. half diagonal is a√2.
The answer is
Initially, the fly at left bottom of square as shown in the diagram walks v Δt along the right side. The fly to the right walks upwards by v Δt. The change in the direction of the fly now is
and it is in the direction of origin. so