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A monic polynomial $p(x)$ of degree 4 has one repeated zero of multiplicity 2 and is divisible by $x^2 + x + 1$ - HSC - SSCE Mathematics Extension 1 - Question 5 - 2020 - Paper 1

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A-monic-polynomial-$p(x)$-of-degree-4-has-one-repeated-zero-of-multiplicity-2-and-is-divisible-by-$x^2-+-x-+-1$-HSC-SSCE Mathematics Extension 1-Question 5-2020-Paper 1.png

A monic polynomial $p(x)$ of degree 4 has one repeated zero of multiplicity 2 and is divisible by $x^2 + x + 1$. Which of the following could be the graph of $p(x)$... show full transcript

Worked Solution & Example Answer:A monic polynomial $p(x)$ of degree 4 has one repeated zero of multiplicity 2 and is divisible by $x^2 + x + 1$ - HSC - SSCE Mathematics Extension 1 - Question 5 - 2020 - Paper 1

Step 1

Identify the properties of the polynomial

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Answer

A monic polynomial of degree 4 means its leading coefficient is 1. The polynomial has a repeated zero of multiplicity 2, indicating at least one factor can be expressed as (xr)2(x - r)^2 for some root rr. Additionally, since it is divisible by x2+x+1x^2 + x + 1, this factor also contributes to the overall degree.

Step 2

Determine the number of zeros

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Answer

The polynomial must have 4 zeros in total. With one zero of multiplicity 2, we are left with 2 more zeros that can either be distinct or repeat a root that has been accounted for. The zeros associated with x2+x+1x^2 + x + 1 are complex and will not affect the degree.

Step 3

Analyze the end behavior of the polynomial

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Answer

Since the polynomial is of degree 4 (an even degree), its end behavior is that as xx approaches both positive and negative infinities, p(x)p(x) approaches positive infinity.

Step 4

Determine characteristics of the graph

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Answer

Given the properties identified: the graph must touch the x-axis at the double root (indicating a local minimum or maximum) and will also feature the behavior corresponding to the complex roots. The graph must not cross the x-axis at the repeated zero.

Step 5

Evaluate the provided graph options

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Answer

By evaluating the characteristics of each graph option (A, B, C, D), option C exhibits a local minimum at the repeated zero while not crossing the x-axis, matching our described properties. Options A, B, and D do not satisfy the conditions for a polynomial with a repeated zero of multiplicity 2.

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