Let the roots of the equation be alpha and beta.
sum of the roots of the quadratic equation ax 2 + bx + c = 0 is equal to the sum of the squares of their reciprocals.
α + β = (1/α2 ) + (1/β2) = (α2 + β2) / (α*β)2 = ((α + β)2 - 2α*β) / (α*β)2
Therefore, Put Sum of roots = - (b/a) and Product of roots is c/a in ((α + β)2 - 2α*β) / (α*β)2
-(b) = ( b2 - 2*(c) ) / (c)2 ...... (Sum of roots = - (b/a) and Product of roots is c/a ....Acc to Vieta's formula for quadratic equation)
-(b) = ( b2 / c2 ) - 2/c
2c = (b2) + b(c2) ............(Divide the equation by abc)
2/b = b/c +c
c/a , a/b and b/c are in AP
So 1/c, b and c/b are in HP.