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
Question 5
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 (x−r)2 for some root r. Additionally, since it is divisible by x2+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+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 x approaches both positive and negative infinities, 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.