Chapter 3: Problem 37
Find all rational zeros of the polynomial, and write the polynomial in factored form. $$P(x)=24 x^{3}+10 x^{2}-13 x-6$$
Short Answer
Expert verified
The rational zero is \( x = \frac{1}{2} \); factored form is \( (x - \frac{1}{2})(x + 1)(3x + 3)\)."
Step by step solution
01
Identify Rational Zero Theorem
The Rational Zero Theorem states that any rational solution \( \frac{p}{q} \) of the polynomial equation \( a_nx^n + a_{n-1}x^{n-1} + \cdots + a_0 \) must be such that \( p \) is a factor of the constant term \( a_0 \), and \( q \) is a factor of the leading coefficient \( a_n \). In this polynomial, the constant term is \(-6\) and the leading coefficient is \(24\).
02
List Possible Rational Zeros
First, list the factors of the constant term \(-6\): \( \pm 1, \pm 2, \pm 3, \pm 6\). Then list the factors of the leading coefficient \(24\): \( \pm 1, \pm 2, \pm 3, \pm 4, \pm 6, \pm 8, \pm 12, \pm 24\). The possible rational zeros are all the fractions of these factors: \( \pm 1, \pm \frac{1}{2}, \pm \frac{1}{3}, \ldots, \pm \frac{6}{24}\).
03
Test Possible Zeros Using Synthetic Division
Use synthetic division to test each possible rational zero. Start with realistic values like \(x = 1\), \(x = -1\), etc. Perform synthetic division to see if the remainder is zero, indicating \(x\) is a root. Through testing, we find that \(x = \frac{1}{2}\) is a root because the remainder is zero.
04
Factor Out the Zero Found
Since \(x = \frac{1}{2}\) is a zero, we can factor \(x - \frac{1}{2}\) out of the polynomial. Using synthetic division, divide \(P(x)\) by \(2x - 1\) (equivalent to multiplying through by 2 to avoid fractions), resulting in \(12x^2 + 16x + 12\).
05
Factor the Quotient Quadratic Polynomial
Now factor the quadratic polynomial \(12x^2 + 16x + 12\). Look for two numbers that multiply to \(12 \times 12 = 144\) and add up to \(16\). After testing pairs, notice that this is reducible by first reducing: \(12(x^2 + \frac{4}{3}x + 1)\), which can be further factored by completing the square or using quadratic formula. This gives \( (2x + 2)(6x + 6) \) after reduction.
06
Write Polynomial in Completely Factored Form
Finally, the fully factored form of \(P(x) = 24x^3 + 10x^2 - 13x - 6\) is \((x - \frac{1}{2})(2x + 2)(6x + 6)\). Simplifying further would give: \(2(x - \frac{1}{2})(x + 1)(3x + 3)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Synthetic Division
Synthetic division is a simplified form of polynomial division, especially useful when dividing by a linear factor. It's quicker and more systematic than traditional polynomial division. We use synthetic division primarily to find roots or zeros of a given polynomial. In synthetic division, the coefficients of the polynomial are written in a horizontal line. We then perform a series of operations to simplify the polynomial and figure out if a certain value is a root.
- Start with the value you're testing as a possible zero. This is placed to the left of the line.
- Write down the coefficients of the polynomial in descending order.
- The first coefficient is brought down unchanged. Use this to multiply the leading tested zero, and write the product under the next coefficient.
- Add down the second column, write the result, and repeat the process.
Factoring Polynomials
Factoring polynomials involves breaking down a polynomial into its component parts, called factors, that when multiplied give the original polynomial. It's a crucial step in simplifying expressions and solving equations. For example, with the polynomial provided, after using synthetic division, we ended up with a simpler quadratic polynomial to factor.
- First, identify any common factors in all terms of the polynomial and factor these out.
- If dealing with a quadratic, look for two numbers that multiply to the product of the leading coefficient and the constant term and add up to the middle term's coefficient.
- Use various factoring techniques such as grouping, using the quadratic formula, or completing the square if necessary.
Quadratic Polynomial
A quadratic polynomial is a second-degree polynomial of the form \( ax^2 + bx + c \). It contains three terms, with the highest degree being two. In the synthetic division process, after finding a root of the original polynomial, one often ends up with a reduced quadratic equation like in the given polynomial problem.
- Quadratic polynomials can often be factored into two binomials, possibly involving irrational numbers, or into linear factors over the complex numbers.
- When it's difficult to factor by inspection, the quadratic formula \( x = \frac{-b \pm \sqrt{b^2-4ac}}{2a} \) may help find the roots.
Polynomial Roots
Polynomial roots, or zeros, are the values of \( x \) for which the polynomial equals zero. They are the solutions to the equation \( P(x) = 0 \). Finding roots is one of the essential aspects of understanding polynomial behavior because roots tell us where the graph of the polynomial crosses the x-axis.
- The Rational Zero Theorem aids in determining possible rational roots by relating them to factors of the constant term and the leading coefficient.
- Testing these possible values through synthetic division helps verify actual roots.
- Once a root (or multiple roots) is found, you can factor the polynomial, which simplifies finding other roots.