Chapter 3: Problem 17
A polynomial \(P\) is given. (a) Find all zeros of \(P\), real and complex. (b) Factor \(P\) completely. $$P(x)=x^{6}-1$$
Short Answer
Expert verified
Zeros are 1, -1, \(\frac{-1 \pm i\sqrt{3}}{2}\), \(\frac{1 \pm i\sqrt{3}}{2}\). Factor: \((x - 1)(x + 1)(x^2 + x + 1)(x^2 - x + 1)\).
Step by step solution
01
Recognize the Polynomial Form
The given polynomial is \(x^6 - 1\). This fits the form \(a^6 - b^6\), which can be factored using the difference of two squares and further factored by recognizing it as a difference of cubes and squares.
02
Apply the Difference of Squares
Start by applying the difference of squares: \(x^6 - 1 = (x^3)^2 - 1^2 = (x^3 - 1)(x^3 + 1)\). This will break the polynomial into two cubic factors which can be further factored.
03
Factor Each Cubic Expression
Factor each of the cubic terms:- \(x^3 - 1\) factors to \((x - 1)(x^2 + x + 1)\) using the formula for the difference of cubes: \(a^3 - b^3 = (a - b)(a^2 + ab + b^2)\).- \(x^3 + 1\) factors to \((x + 1)(x^2 - x + 1)\) using the formula for the sum of cubes: \(a^3 + b^3 = (a + b)(a^2 - ab + b^2)\).
04
Form the Completely Factored Polynomial
Combine the factors from the cubic expressions to completely factor \(x^6 - 1\): \(P(x) = (x - 1)(x^2 + x + 1)(x + 1)(x^2 - x + 1)\).
05
Solve for the Zeros
Set each factor to zero to find all zeros of \(P(x)\).- \(x - 1 = 0\) gives \(x = 1\).- \(x + 1 = 0\) gives \(x = -1\).- Solve \(x^2 + x + 1 = 0\) using the quadratic formula: \[x = \frac{-1 \pm i\sqrt{3}}{2}\]- Solve \(x^2 - x + 1 = 0\) also using the quadratic formula: \[x = \frac{1 \pm i\sqrt{3}}{2}\]
06
Compile the Zeros and Factors
The real zeros are \(x = 1\) and \(x = -1\). The complex zeros stemming from \(x^2 + x + 1\) are: \(x = \frac{-1 \pm i\sqrt{3}}{2}\), and from \(x^2 - x + 1\) are: \(x = \frac{1 \pm i\sqrt{3}}{2}\). The factorized polynomial is \(P(x) = (x - 1)(x^2 + x + 1)(x + 1)(x^2 - x + 1)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Difference of Squares
The **difference of squares** is a powerful algebraic tool used to simplify expressions. It applies to any expression of the form \(a^2 - b^2\), which can be factored into \((a - b)(a + b)\). This simplification is used because it breaks down a degree-two polynomial into two linear terms.
For example, in the original problem, the expression \(x^6 - 1\) can be recognized as a difference of squares since it fits the form \((x^3)^2 - 1^2\).
This allows us to factor it into \((x^3 - 1)(x^3 + 1)\).
**Key Points:**
For example, in the original problem, the expression \(x^6 - 1\) can be recognized as a difference of squares since it fits the form \((x^3)^2 - 1^2\).
This allows us to factor it into \((x^3 - 1)(x^3 + 1)\).
**Key Points:**
- Recognize expressions in the form \(a^2 - b^2\).
- Break them down into \((a - b)(a + b)\).
- Factoring makes solving polynomials easier by reducing their degree.
Difference of Cubes
In algebra, the **difference of cubes** formula helps to factor expressions like \(a^3 - b^3\). The general formula is \(a^3 - b^3 = (a - b)(a^2 + ab + b^2)\).
This method can simplify complex polynomials into more manageable parts. In the polynomial \(x^3 - 1\) from the problem, we apply the difference of cubes formula.
The term \(x^3 - 1\) can thus be factored as \((x - 1)(x^2 + x + 1)\).
**Key Points:**
This method can simplify complex polynomials into more manageable parts. In the polynomial \(x^3 - 1\) from the problem, we apply the difference of cubes formula.
The term \(x^3 - 1\) can thus be factored as \((x - 1)(x^2 + x + 1)\).
**Key Points:**
- Identify an expression that is a difference of cubes.
- Use the formula, substituting \(a\) and \(b\) with appropriate values.
- Factor into a linear term and a quadratic term.
Complex Zeros
**Complex zeros** are the roots of a polynomial that are not real numbers, often involving imaginary units. When factoring polynomials, especially of higher degrees, it's common to encounter non-real roots.
The imaginary unit \(i\) satisfies \(i^2 = -1\), allowing the solution of quadratic equations that don't have real solutions.
For instance, when solving \(x^2 + x + 1 = 0\), the quadratic formula reveals complex zeros:
**Understanding Zeros:**
The imaginary unit \(i\) satisfies \(i^2 = -1\), allowing the solution of quadratic equations that don't have real solutions.
For instance, when solving \(x^2 + x + 1 = 0\), the quadratic formula reveals complex zeros:
- Apply the quadratic formula: \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\).
- For \(x^2 + x + 1 = 0\), this results in \(x = \frac{-1 \pm i\sqrt{3}}{2}\).
**Understanding Zeros:**
- Real zeros are the roots located on the real number line.
- Complex zeros include imaginary components and appear in conjugate pairs.
- Identifying them is key to completely factoring polynomials.