How to find in terms of b and d a quadratic equation satisfied by the possible ratios of the progression?

Find a condition for the roots of the equation x^3 - 3bx^2 +3cx - d = 0 to be in geometric progression. Find in terms of b and d a quadratic equation satisfied by the possible ratios of the progression.

I already solve the 1st part by finding the condition which is b^3 x d = c^3. I don't understand the 2nd part of the question at all. How to solve it?

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