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Ch. 3 - Polynomial and Rational Functions
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Not the one you use?Change textbook
All textbooksBlitzer 8th EditionCh. 3 - Polynomial and Rational FunctionsProblem 39
Chapter 4, Problem 39

Use the Intermediate Value Theorem to show that each polynomial has a real zero between the given integers. f(x)=3x3−10x+9; between -3 and -2

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Recall the Intermediate Value Theorem (IVT), which states that if a function \( f(x) \) is continuous on a closed interval \([a, b]\) and \( f(a) \) and \( f(b) \) have opposite signs, then there exists at least one real number \( c \) in \((a, b)\) such that \( f(c) = 0 \).
Identify the function and the interval: \( f(x) = 3x^3 - 10x + 9 \), and the interval is \([-3, -2]\).
Evaluate \( f(x) \) at the endpoints of the interval: calculate \( f(-3) = 3(-3)^3 - 10(-3) + 9 \) and \( f(-2) = 3(-2)^3 - 10(-2) + 9 \).
Determine the signs of \( f(-3) \) and \( f(-2) \). If one is positive and the other is negative, then by the IVT, there is at least one zero between \(-3\) and \(-2\).
Conclude that since \( f(x) \) is a polynomial (and thus continuous everywhere) and the function values at \(-3\) and \(-2\) have opposite signs, there must be a real zero of \( f(x) \) between \(-3\) and \(-2\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Intermediate Value Theorem

The Intermediate Value Theorem states that if a function is continuous on a closed interval [a, b] and takes values f(a) and f(b) at each end, then it must take any value between f(a) and f(b) at some point within the interval. This theorem is used to prove the existence of roots by showing the function changes sign.
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Polynomial Continuity

Polynomials are continuous functions for all real numbers, meaning there are no breaks, jumps, or holes in their graphs. This continuity ensures that the Intermediate Value Theorem can be applied to polynomials on any interval, making it possible to locate zeros by checking function values at interval endpoints.
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Evaluating Function Values at Given Points

To apply the Intermediate Value Theorem, you must calculate the polynomial's values at the given integers (here, -3 and -2). If the function values have opposite signs, it indicates the function crosses the x-axis between those points, confirming the existence of a real zero in that interval.
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Related Practice
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