AlgebraDifficulty 3.8AMC 10/12Find the answerItaly
Let P(x)=x3+ax2+bx+c. Given that the sum of two of the roots of the polynomial equals zero, which of the following relations among the coefficients of P(x) is always true?
Pick one
Solution
Solution:
The answer is (B). Let x0, x1 and −x1 be the roots of the polynomial; it must hold, for every x, that (x−x0)(x−x1)(x+x1)=x3+ax2+bx+c. Expanding the products and equating the coefficients of the terms of the same degree (principle of identity of polynomials), we get −x0=a, −x12=b, x12x0=c, from which ab=c.
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Source: MathNet,
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