If P is any arbitrary point on the circumcircle of the equilateral triangle of side length l units then |→PA|2+|→PB|2+|→PC|2 is always equal to
A tube U - shaped has a uniform cross - section with arm length l1 and l2(l1>l2). Tube has a liquid of density ρ1 filled to a height h. Another liquid of density ρ2=ρ12 is poured in arm . Both liquids are immiscible. The length of the second liquid that should be poured in A so that first overtone of is in unison with fundamental tone of B is