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Correct answer: 2
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Let We need an integer such that all real roots of lie in .
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Rewrite the polynomial in a useful form. Using we get This is not exactly , so instead observe: P(x)=(x+1)^5+igl(x^5+5x^3+5x^2+5x+9igr), which is not especially helpful. So let us analyze roots directly.
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First, determine how many real roots can have. Differentiate: Now factor: Hence, and in fact only at . Therefore is an increasing function on (non-decreasing everywhere, strictly increasing except for a stationary point at ). So can have at most one real root.
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Now locate that real root by checking values. Compute: Next, Since is continuous, there is a real root in .
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Because has at most one real root and we have found one in , this is the only real root, and hence all real roots lie in the interval Thus, Therefore,
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Compare with the stored correct answer. Stored correct answer = , which matches our result.
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