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imc

algebra intermediate

Problem

Let , , and be the distinct roots of the polynomial . It is given that there exist real numbers , , and such that for all . What is ?
(A)
(B)
(C)
(D)
Solution
Multiplying both sides by yields As this is a polynomial identity, and it is true for infinitely many , it must be true for all (since a polynomial with infinitely many roots must in fact be the constant polynomial ). This means we can plug in to find that . Similarly, we can find and . Summing them up, we get that We can express , and by Vieta's Formulas, we know that this expression is equal to . Vieta's also gives (which we also used to find ), so the answer is . Note: this process of substituting in the 'forbidden' values in the original identity is a standard technique for partial fraction decomposition, as taught in calculus classes.
Final answer
B