How do we solve a quadratic inequality with multiple factors?

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Discussion Overview

The discussion revolves around solving a quadratic inequality with multiple factors, specifically the inequality (x^4)(x - 2)(x - 16) ≥ 0. Participants explore methods for identifying critical points and testing intervals to determine the solution set.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant suggests setting each factor to 0 to find values of x and proposes plotting these on a number line for testing.
  • Another participant notes that the root x=0 has even multiplicity, indicating that the sign of the expression does not change across this root, while the roots x=2 and x=16 have odd multiplicity, suggesting that the sign will change across these points.
  • A participant identifies the critical points as x = 0, x = 2, and x = 16, and includes these points in their analysis.
  • Testing intervals, one participant finds that the expression is true for (-infinity, 0), (0, 2), and (16, infinity), but false for (2, 16), leading to a proposed solution of (-infinity, 2] U [16, infinity).

Areas of Agreement / Disagreement

Participants appear to agree on the method of finding critical points and testing intervals, but there is no explicit consensus on the final solution as participants have not confirmed the correctness of the proposed solution.

Contextual Notes

Some assumptions regarding the behavior of the function at critical points and the implications of multiplicity are present but not fully explored or resolved.

mathdad
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This is the last quadratic inequality problem (for now) before moving on to Chapter 3, Section 3.1 THE DEFINITION OF A FUNCTION.

Section 2.6
Question 30

Solve the quadratic inequality.

(x^4)(x - 2)(x - 16) ≥ 0

Do I set each factor to 0 and solve for x? The values of x are then plotted on the number line for testing.

Correct?
 
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RTCNTC said:
This is the last quadratic inequality problem (for now) before moving on to Chapter 3, Section 3.1 THE DEFINITION OF A FUNCTION.

Section 2.6
Question 30

Solve the quadratic inequality.

(x^4)(x - 2)(x - 16) ≥ 0

Do I set each factor to 0 and solve for x? The values of x are then plotted on the number line for testing.

Correct?

Yes, observe that the root $x=0$ is of even multiplicity (4), and so the sign of the expression will not change across this root. The others are of odd multiplicity (1) and so the sign will change across those roots.
 
I will work on this tomorrow. Working right now.
 
(x^4)(x - 2)(x - 16) ≥ 0

Our critical points are x = 0, x = 2 and x = 16.

I can see that our critical points are also included.

<-------(0)--------(2)--------(16)------>

For (-infinity, 0), let x = -1. True statement.

For (0, 2), let x = 1. True statement.

For (2, 16), let x = 3. False statement.

For (16, infinity), let x = 4. True statement.

Solution:

(-infinity, 2] U [16, infinity)

Correct?
 
Last edited:

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