Chapter 3: Problem 16
Find all rational zeros of the polynomial, and write the polynomial in factored form. $$P(x)=x^{3}-7 x^{2}+14 x-8$$
Short Answer
Expert verified
The rational zeros are \(1, 2,\) and \(4\); the polynomial in factored form is \((x-1)(x-2)(x-4)\).
Step by step solution
01
Identify possible rational zeros
To find the possible rational zeros of the polynomial \( P(x) = x^3 - 7x^2 + 14x - 8 \), we apply the Rational Root Theorem. This theorem states that any rational zero, expressed as a fraction \( \frac{p}{q} \), is such that \( p \) is a factor of the constant term and \( q \) is a factor of the leading coefficient. The constant term here is \(-8\) and the leading coefficient is \(1\). Therefore, the possible rational zeros are the factors of \(-8\), which are \( \pm 1, \pm 2, \pm 4, \pm 8 \).
02
Test the possible rational zeros
We substitute each possible rational zero into \( P(x) \) to determine if it is indeed a zero of the polynomial.- \( P(1) = 1^3 - 7 \cdot 1^2 + 14 \cdot 1 - 8 = 0 \) (So, \( x = 1 \) is a zero.)- \( P(-1) = (-1)^3 - 7 \cdot (-1)^2 + 14 \cdot (-1) - 8 = -30 \)- \( P(2) = 2^3 - 7 \cdot 2^2 + 14 \cdot 2 - 8 = 0 \) (So, \( x = 2 \) is a zero.)- \( P(-2) = (-2)^3 - 7 \cdot (-2)^2 + 14 \cdot (-2) - 8 = -64 \)- \( P(4) = 4^3 - 7 \cdot 4^2 + 14 \cdot 4 - 8 = 0 \) (So, \( x = 4 \) is a zero.)- Since \( x = 8 \) and \( x = -8 \) yield very large non-zero values, these calculations are omitted for brevity.
03
Factor the polynomial using found zeros
We found that \( x = 1, 2, 4 \) are zeros of the polynomial. Therefore, \( P(x) \) can be factored using these zeros: - Use the zero \( x = 1 \) to factor as \( (x - 1) \).- Use the zero \( x = 2 \) to further factor as \( (x - 2) \).- Use the zero \( x = 4 \) to complete the factorization as \( (x - 4) \). Thus, the polynomial in factored form is \( P(x) = (x - 1)(x - 2)(x - 4) \).
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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 profound yet easy method to narrow down the potential rational zeros (roots) of a polynomial. This theorem proposes that if you have a polynomial equation with integer coefficients, any potential rational root also has to be a fraction that can be formed by dividing a factor of the constant term by a factor of the leading coefficient. In simpler terms, let's say you have a polynomial like \( P(x) = x^3 - 7x^2 + 14x - 8 \). Here, the constant term is \(-8\) and the leading coefficient is \(1\).
Following the theorem:
Following the theorem:
- The factors of the constant term \(-8\) are \( \pm 1, \pm 2, \pm 4, \pm 8\).
- The factors of the leading coefficient \(1\) are just \( \pm 1\).
polynomial factorization
Once you identify the zeros of a polynomial using concepts like the Rational Root Theorem, you can begin the process of factorization. Factorization involves expressing the polynomial as a product of its simpler factors. For example, after finding the zeros for the polynomial \( P(x) = x^3 - 7x^2 + 14x - 8 \), you can write it in its factored form.
Firstly, suppose we found zeros at \( x = 1, 2, 4 \) through substituting and testing possible values. Each of these corresponds to a factor of the polynomial:
Firstly, suppose we found zeros at \( x = 1, 2, 4 \) through substituting and testing possible values. Each of these corresponds to a factor of the polynomial:
- \( x = 1 \) gives \( (x - 1) \).
- \( x = 2 \) gives \( (x - 2) \).
- \( x = 4 \) gives \( (x - 4) \).
polynomials
Polynomials are algebraic expressions that consist of variables and coefficients, connected using addition, subtraction, multiplication, and non-negative integer exponents. Take, for instance, \( x^3 - 7x^2 + 14x - 8 \), which is a cubic polynomial because the highest exponent is 3.
Polynomials have several characteristics:
Polynomials have several characteristics:
- **Degree:** The highest power (exponent) in a polynomial. This also tells us the maximum number of roots and turning points the polynomial can have.
- **Terms:** Parts of the polynomial separated by plus or minus signs. Each term consists of a coefficient and a variable raised to an exponent.
- **Coefficients:** Numbers that multiply the variables in each term, like \(-7\) in \(-7x^2\).