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jmc

algebra intermediate

Problem

The three roots of the cubic are distinct real numbers strictly between and . If the roots are , , and , what is the sum
Solution
Since are roots of , are roots of .

If we consider only the constant terms in the expansion of the above polynomial, we find that the constant coefficient is . Similarly, the linear coefficient of the above polynomial is

Hence, are the roots of a cubic in the reversed form . Using Vieta's formula,
Final answer
12