Chapter 0: Problem 71
Factor completely, or state that the polynomial is prime. $$x^{3}+2 x^{2}-9 x-18$$
Short Answer
Expert verified
The completely factored form of the polynomial \(x^{3} + 2x^{2} - 9x - 18\) is \((x+3)(x-1)(x-6)\).
Step by step solution
01
Find the roots
First, apply the rational root theorem, which suggests that if \(p/q\) is a rational root of the polynomial equation \(x^{3} + 2x^{2} - 9x -18 = 0\), then p is a factor of the constant term '-18' and q is a factor of the coefficient '1' of \(x^{3}\). Possible rational roots of the equation are ±1, ±2, ±3, ±6, ±9, ±18.
02
Substitute Possible Roots
Substitute each possible root in the polynomial equation. If a possible root, when substituted in the place of x, makes the equation true (i.e., the left side equal to the right side), then that is indeed a root of the equation. By substituting, it is found that '-3', '1', and '6' are roots of the equation.
03
Factoring the Polynomial
Knowing that '-3', '1', and '6' are roots of the equation, the original polynomial equation can now be written as the product of the three binomials \(x - root\). So the factored form of the polynomial equation \(x^{3} + 2x^{2} - 9x - 18 = 0\) will be \((x+3)(x-1)(x-6)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Rational Root Theorem
The Rational Root Theorem is a valuable tool for finding the roots of polynomial equations, specifically rational roots. It applies to polynomials with rational coefficients and states that any potential rational root \( \frac{p}{q} \), where \( p \) is a factor of the constant term and \( q \) is a factor of the leading coefficient. This theorem narrows down the possibilities for finding the roots, making the process more efficient.
Let's consider a polynomial such as \( x^3 + 2x^2 - 9x - 18 \). According to the Rational Root Theorem, the potential rational roots are based on the factors of the constant term (-18) and the leading coefficient (1). Thus, the possible rational roots are ±1, ±2, ±3, ±6, ±9, and ±18.
Let's consider a polynomial such as \( x^3 + 2x^2 - 9x - 18 \). According to the Rational Root Theorem, the potential rational roots are based on the factors of the constant term (-18) and the leading coefficient (1). Thus, the possible rational roots are ±1, ±2, ±3, ±6, ±9, and ±18.
- The value 'p' represents possible divisors of the constant term.
- The value 'q' represents possible divisors of the leading coefficient.
Roots of Polynomial
Identifying the roots of a polynomial is an essential step in polynomial factorization. Roots are simply values of \( x \) for which the polynomial evaluates to zero. Finding these roots transforms the polynomial into simpler algebraic factors using the roots themselves.
For the polynomial \( x^3 + 2x^2 - 9x - 18 \), possible roots derived from using the Rational Root Theorem were ±1, ±2, ±3, ±6, ±9, and ±18. By substituting these into the polynomial and calculating, we determine that '-3', '1', and '6' are actual roots. This means when substituted, they zero out the polynomial. These roots play a pivotal role in the factorization process.
For the polynomial \( x^3 + 2x^2 - 9x - 18 \), possible roots derived from using the Rational Root Theorem were ±1, ±2, ±3, ±6, ±9, and ±18. By substituting these into the polynomial and calculating, we determine that '-3', '1', and '6' are actual roots. This means when substituted, they zero out the polynomial. These roots play a pivotal role in the factorization process.
- Roots are the solution of the polynomial equation when set to zero.
- Substituting verified roots simplifies the overall factorization process.
Factoring Polynomials
Factoring polynomials is the process of breaking down a polynomial into a product of its simpler factors. Once the roots are determined, we can express the polynomial as a product of binomials associated with these roots.
Given the polynomial \( x^3 + 2x^2 - 9x - 18 \) and the confirmed roots '-3', '1', and '6', we can factor the polynomial into \((x+3)(x-1)(x-6)\). Each root corresponds to a factor, expressed as \( x - \text{root} \), simplifying the complex polynomial.
Given the polynomial \( x^3 + 2x^2 - 9x - 18 \) and the confirmed roots '-3', '1', and '6', we can factor the polynomial into \((x+3)(x-1)(x-6)\). Each root corresponds to a factor, expressed as \( x - \text{root} \), simplifying the complex polynomial.
- Factoring requires identification of each root as a simple binomial factor.
- This method provides a fully factored form that represents the same polynomial.
- Factoring is crucial for simplifying polynomials and solving equations.