Chapter 3: Problem 244
For the following exercises, find the \(x\) - or \(t\) -intercepts of the polynomial functions. $$ f(x)=x^{6}-3 x^{4}-4 x^{2} $$
Short Answer
Expert verified
The x-intercepts are \(x = 0, 2, -2\).
Step by step solution
01
Set the Polynomial Equal to Zero
To find the x-intercepts of the polynomial, we first set the function equal to zero: \(f(x) = x^6 - 3x^4 - 4x^2 = 0\). This equation represents the points where the polynomial crosses the x-axis.
02
Factor Out the Greatest Common Factor
Notice that \(x^2\) is a common factor in the polynomial. We can factor it out: \(x^2(x^4 - 3x^2 - 4) = 0\). This gives us two factors to consider: \(x^2 = 0\) and \(x^4 - 3x^2 - 4 = 0\).
03
Solve the Equation from the First Factor
The first factor is \(x^2 = 0\). Solving for \(x\) gives \(x = 0\). So, \(x = 0\) is one intercept of the polynomial.
04
Factor the Quadratic in the Second Factor
The remaining polynomial is \(x^4 - 3x^2 - 4\). We use substitution to simplify: let \(y = x^2\), then our equation becomes \(y^2 - 3y - 4 = 0\).
05
Solve the Quadratic Equation
We factor the quadratic \(y^2 - 3y - 4\) into \((y - 4)(y + 1) = 0\). Solving gives \(y = 4\) and \(y = -1\).
06
Back-Substitute and Solve for x
Return to the original variable by substituting back \(y = x^2\). Thus, \(x^2 = 4\) and \(x^2 = -1\). Solving \(x^2 = 4\) gives \(x = 2\) and \(x = -2\). Since \(x^2 = -1\) gives imaginary solutions, we only consider real roots. Therefore, the x-intercepts are \(x = 0\), \(x = 2\), and \(x = -2\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Factoring Polynomials
Factoring polynomials is a crucial skill when solving polynomial equations and finding their intercepts. It involves breaking down a polynomial into a product of smaller, simpler polynomials. This process makes it easier to identify the roots or solutions of the polynomial equation. In our example, the polynomial \(f(x) = x^6 - 3x^4 - 4x^2\) is first set to zero to find the x-intercepts. We identified that \(x^2\) is a common factor that can be extracted from every term of the polynomial, simplifying our task. Factoring simplifies the polynomial into \(x^2(x^4 - 3x^2 - 4)\), allowing us to tackle each factor separately. Key steps in factoring include:
- Identifying common factors in the terms
- Extracting these factors to simplify the polynomial
- Breaking the polynomial into smaller quadratics to solve
Quadratic Equations
Quadratic equations are polynomials of the form \(ax^2 + bx + c = 0\). In this exercise, we reduced the polynomial to a quadratic equation through a clever substitution. We replaced \(x^2\) with \(y\), transforming \(x^4 - 3x^2 - 4 = 0\) into \(y^2 - 3y - 4 = 0\). This method converts a higher degree polynomial into a more familiar quadratic equation, which is easier to solve. Once in quadratic form, we factor \(y^2 - 3y - 4\) into \((y-4)(y+1) = 0\). Solving this gives the solutions for \(y\):
- \(y = 4\)
- \(y = -1\)
- Factoring
- Using the quadratic formula
- Completing the square
Real Roots
Real roots of a polynomial are the x-values where the polynomial equals zero. These represent the x-intercepts of the polynomial graph. By solving for the real roots, we find where the polynomial crosses the x-axis. For \(f(x) = x^6 - 3x^4 - 4x^2\), our factored polynomial \(x^2(x^4 - 3x^2 - 4)\) provided two separate equations. Solving \(x^2 = 0\) easily gives us a real root of \(x = 0\). When solving the quadratic \(y^2 - 3y - 4 = 0\) and substituting back to \(x^2 = y\), \(x^2 = 4\) gave real roots of \(x = 2\) and \(x = -2\).The importance of identifying real roots lies in their practical interpretation, as they signify points of intersection between the polynomial graph and the x-axis, something greatly useful in both theoretical and applied math.
Common Factors
Identifying common factors in a polynomial is an essential starting point for simplifying and solving it. A common factor is a term that divides each part of the polynomial with no remainder. Recognizing these can significantly simplify the complexity of the initial polynomial equation. In this exercise, \(x^2\) was a common factor among all terms in \(f(x) = x^6 - 3x^4 - 4x^2\). By extracting \(x^2\), we transformed the polynomial into \(x^2(x^4 - 3x^2 - 4)\), effectively breaking it into parts that are much easier to manage.Understanding how to factor using common factors includes:
- Scanning the polynomial for terms that are present in each element
- Factoring them out, providing a new, simpler polynomial
- Makes further breakdown into quadratic equations achievable