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Finding a Polynomial Function with Given Zeros, find a polynomial function with real coefficients that has the given zeros. (There are many correct answers.) $$\frac{2}{3},-1,3+\sqrt{2} i$$

Short Answer

Expert verified
The polynomial function with given zeros is \(f(x) = x^4 - \frac{8}{3}x^3 + \frac{31}{3}x^2 - 20x + 4\).

Step by step solution

01

Consider Complex Conjugate

Identify the complex root \(3+\sqrt{2}i\) and include its conjugate pair \(3-\sqrt{2}i\) among the roots.
02

Form the Factors

Transform each root into a factor of the polynomial by setting \(x\) equal to the zero and rearranging the equation to equal zero. This gives the factors as; \[x - \frac{2}{3}\], \(x + 1\), \(x -(3+\sqrt{2}i)\) and \(x -(3-\sqrt{2}i)\] respectively.
03

Multiply the Factors

Multiply all the factors together. The multiplication will yield an expression for the polynomial function when the complex roots are factored in the form \(x^2 - (a+b)x + (a^2 + b^2)\). Doing this yields;\[(x - \frac{2}{3})(x + 1)((x - 3)^2 + (\sqrt{2})^2)\] After performing the algebra, we get;\[f(x) = x^4 - \frac{8}{3}x^3 + \frac{31}{3}x^2 - 20x + 4\].
04

Check the result

To verify whether the formula obtained is correct or not, substitute the zeros into the polynomial function obtained and check that it equals zero.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Complex Conjugate Roots
When working with polynomial functions that have real coefficients, acknowledging the concept of complex conjugate roots is crucial. If you have a complex number as a root, say \(3 + \sqrt{2}i\), its complex conjugate \(3 - \sqrt{2}i\) must also be a root... if the polynomial has real coefficients. This is because complex roots always appear in conjugate pairs in such cases.

Understanding complex conjugate roots means remembering a few key points:
  • They ensure that all coefficients of a polynomial remain real numbers.
  • If one complex root is present, its conjugate guarantees keeping the polynomial balanced in terms of real number representation.
  • Handling these roots typically involves multiplying their respective binomials together.
Real Coefficients
Real coefficients are the hallmark of many polynomial equations, especially in applied mathematics and physical sciences. A polynomial with real coefficients is one where all the values multiplying the powers of \(x\) are real numbers, including fractions and whole numbers.

Important aspects to consider with real coefficients include:
  • Every complex root must be paired with its conjugate to maintain real coefficients.
  • This pairing is essential because it prevents coefficients from becoming imaginary or complex.
  • The presence of only real numbers means the polynomial represents scenarios accessible within the real number system.
Whenever creating or solving for polynomials with real roots, always verify that all terms remain rooted in real numbers to satisfy this condition.
Zeros of a Polynomial
Zeros, or roots, of a polynomial are the values of \(x\) that make the polynomial equal zero. Identifying these zeros is a fundamental step in understanding the behavior of polynomial functions. In polynomials with real coefficients, zeros can be:
  • Real numbers, such as integers or fractions.
  • Complex numbers, which will always come in conjugate pairs if the coefficients are real.
Once zeros are known, they help in constructing the full polynomial. They show how the graph of the polynomial will behave and where it will cross the \(x\)-axis. By forming each zero into a factor, you can multiply these factors together to obtain the polynomial equation. For instance, given zeros: \(\frac{2}{3}\), \(-1\), \(3+\sqrt{2}i\), and \(3-\sqrt{2}i\), the polynomial would be formed step by step to maintain real coefficients, ultimately yielding a functional expression that models the data or scenario in question.

Knowing the zeros allows one to easily evaluate polynomial behavior, check qualities like symmetry, and understand intersections with the number line.

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Most popular questions from this chapter

Graphical Analysis In Exercises \(63-66,\) use a graphing utility to graph the rational function. State the domain of the function and find any asymptotes. Then zoom out sufficiently far so that the graph appears as a line. Identify the line. $$f(x)=\frac{2 x^{2}+x}{x+1}$$

Sales After discontinuing all advertising for a tool kit in 2007 , the manufacturer noted that sales began to drop according to the model $$S=\frac{500,000}{1+0.4 e^{k t}}$$ where \(S\) represents the number of units sold and \(t=7\) represents \(2007 .\) In \(2011,300,000\) units were sold. (a) Complete the model by solving for \(k\) . (b) Estimate sales in \(2015 .\)

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Rational and Irrational Zeros, match the cubic function with the numbers of rational and irrational zeros. (a) Rational zeros: \(0 ;\) irrational zeros: 1 (b) Rational zeros: \(3 ;\) irrational zeros: 0 (c) Rational zeros: \(1 ;\) irrational zeros: 2 (d) Rational zeros: \(1 ;\) irrational zeros: 0 $$f(x)=x^{3}-2$$

Population The populations \(P\) (in thousands) of Horry County, South Carolina, from 1980 through 2010 can be modeled by $$P=20.6+85.5 e^{0.0360 t}$$ where \(t\) represents the year, with \(t=0\) corresponding to \(1980 .\) (Source: U.S. Census Bureau) (a) Use the model to complete the table. (b) According to the model, when will the population of Horry County reach \(350,000 ?\) (c) Do you think the model is valid for long-term predictions of the population? Explain.

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