Chapter 4: Problem 69
For each polynomial at least one zero is given. Find all others analytically. $$P(x)=-x^{3}+8 x^{2}+3 x-24 ; \quad 8$$
Short Answer
Expert verified
The zeros of the polynomial are \( x = 8, x = \sqrt{3}, x = -\sqrt{3} \).
Step by step solution
01
Understand the Problem
The polynomial given is \( P(x) = -x^3 + 8x^2 + 3x - 24 \). We know one zero of the polynomial is \( x = 8 \). We need to find the other zeros analytically.
02
Use the Given Zero
Since \( x = 8 \) is a zero, \( (x - 8) \) is a factor of \( P(x) \). We can use synthetic division to divide \( P(x) \) by \( (x - 8) \) to find the quotient polynomial.
03
Perform Synthetic Division
Set up synthetic division with \( 8 \) and the coefficients of \( P(x) \): \([-1, 8, 3, -24]\).Perform the division: \[\begin{array}{r|rrrr} 8 & -1 & 8 & 3 & -24 \ & & -8 & 0 & 24 \ \hline & -1 & 0 & 3 & 0 \ \end{array}\]The quotient is \( -1x^2 + 0x + 3 \), which simplifies to \( -x^2 + 3 \). No remainder means the division is exact.
04
Factor the Quotient
The quotient \( -x^2 + 3 \) can be rewritten as \( -(x^2 - 3) \). Factoring \( x^2 - 3 \), we get \( (x - \sqrt{3})(x + \sqrt{3}) \). Therefore, the factors of the quotient are \( (x - \sqrt{3}) \) and \( (x + \sqrt{3}) \).
05
Find All Zeros
Combine the zero and factors: The polynomial is effectively \( (x - 8)(x - \sqrt{3})(x + \sqrt{3}) \). Thus, the zeros are \( x = 8, x = \sqrt{3}, x = -\sqrt{3} \).
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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 way to divide polynomials, particularly when you need to divide by a linear expression of the form \(x - c\). In this problem, since we know that \(x = 8\) is a zero of the polynomial \(-x^3 + 8x^2 + 3x - 24\), we can use synthetic division to factor \((x - 8)\) out of the polynomial.
To begin synthetic division, list the coefficients of the polynomial in descending order. For the given polynomial, these are \(-1\), \(8\), \(3\), and \(-24\). Next, write the zero \(8\) to the left and initiate the division process:
To begin synthetic division, list the coefficients of the polynomial in descending order. For the given polynomial, these are \(-1\), \(8\), \(3\), and \(-24\). Next, write the zero \(8\) to the left and initiate the division process:
- Bring down the leading coefficient, \(-1\), to the bottom row.
- Multiply it by \(8\) and place the result, \(-8\), under the next coefficient.
- Add these numbers up to get the new bottom row entry, repeat the multiplication, continue until the end.
- The final line represents the coefficients of the quotient polynomial.
Factoring Polynomials
Factoring a polynomial refers to breaking it down into a product of simpler polynomials. This is crucial for finding the roots or zeros of the polynomial. With our problem, after using synthetic division, the polynomial \(-x^3 + 8x^2 + 3x - 24\) was reduced to \(-x^2 + 3\).
To factor \(-x^2 + 3\), we first consider it as \(-1\cdot(x^2 - 3)\). We focus on \(x^2 - 3\) since it's a difference of squares type, which takes the form \((x - a)(x + a)\) where \(a = \sqrt{3}\).
To factor \(-x^2 + 3\), we first consider it as \(-1\cdot(x^2 - 3)\). We focus on \(x^2 - 3\) since it's a difference of squares type, which takes the form \((x - a)(x + a)\) where \(a = \sqrt{3}\).
- This means \(x^2 - 3 = (x - \sqrt{3})(x + \sqrt{3})\).
Quadratic Equation
A quadratic equation is a second-degree polynomial equation in the form \(ax^2 + bx + c = 0\). In this scenario, the polynomial \(-x^2 + 3 = 0\) represents a type of quadratic where the linear term \(b\) is absent. This means it's simpler to solve using factoring or by rearranging terms.
Here, since \(-x^2 + 3 = 0\) can be seen through the lens of rearranging terms, we get \(x^2 = 3\). Solving for \(x\), we take the square root of both sides, giving us two solutions:
Here, since \(-x^2 + 3 = 0\) can be seen through the lens of rearranging terms, we get \(x^2 = 3\). Solving for \(x\), we take the square root of both sides, giving us two solutions:
- \(x = \sqrt{3}\)
- \(x = -\sqrt{3}\)