Chapter 6: Problem 103
The area of a teacher's desktop is represented by the trinomial \(\left(4 x^{2}+20 x-11\right)\) in. \(2^{2} .\) Factor it to find the polynomials that represent its length and width.
Short Answer
Expert verified
The trinomial factors as \((2x - 1)(2x + 11)\).
Step by step solution
01
Identify the Trinomial Coefficients
The trinomial given is \(4x^2 + 20x - 11\). Here, \(a = 4\), \(b = 20\), and \(c = -11\). These coefficients are part of the standard quadratic form \(ax^2 + bx + c\).
02
Use the Quadratic Formula for Roots
Since the trinomial's factors represent area dimensions, start by finding roots with the quadratic formula: \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\). Substitute the values: \(b = 20\), \(a = 4\), \(c = -11\).
03
Calculate the Discriminant
Calculate the discriminant as \(b^2 - 4ac = 20^2 - 4 \cdot 4 \cdot (-11) = 400 + 176 = 576\). A positive discriminant confirms two real roots, allowing factorization.
04
Find the Roots
Apply the quadratic formula: \(x = \frac{-20 \pm \sqrt{576}}{8}\). Simplifying, \(x = \frac{-20 \pm 24}{8}\). Hence, the roots are \(x = \frac{4}{8}=0.5\) and \(x = \frac{-44}{8}=-5.5\).
05
Express the Trinomial in Factorized Form
With roots 0.5 and -5.5, the trinomial factors to \((x - 0.5)(x + 5.5)\). However, since the leading coefficient is not 1, check for integer factors of \(4\cdot(-11) = -44\) and rearrange terms into full polynomials.
06
Final Factorization with Integer Coefficients
Rewrite \(4x^2 + 20x - 11\) as \((2x + a)(2x + b)\) knowing calculated roots were simplified. After testing factor pairs, factor to aimed polynomials \((2x - 1)(2x + 11)\).
07
Verification
Multiply \((2x - 1)(2x + 11)\) back: \((2x - 1)(2x + 11) = 4x^2 + 22x - 2x - 11 = 4x^2 + 20x - 11\). The trinomial matches, confirming correct factors.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Formula
The quadratic formula is a powerful tool for solving quadratic equations, particularly useful when polynomial factorization is not straightforward. A quadratic equation is generally expressed as \(ax^2 + bx + c = 0\), where \(a\), \(b\), and \(c\) are coefficients. To solve for \(x\), the quadratic formula is used:\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}.\]This formula calculates the roots of the quadratic equation. These roots are where the graph of the quadratic equation intersects the x-axis. Depending on the discriminant \(b^2 - 4ac\), you can determine the nature of the roots:
- If the discriminant is positive, there are two distinct real roots.
- If it is zero, there is exactly one real root (also known as a repeated or double root).
- If the discriminant is negative, the roots are complex conjugates and not real.
Discriminant
The discriminant is a key concept within the quadratic formula, found in the expression \(b^2 - 4ac\). It provides valuable information about the nature and number of roots associated with a quadratic equation:
- A positive discriminant indicates two distinct real roots, which means the quadratic can be factored over the reals.
- A discriminant of zero indicates one real, repeated root.
- A negative discriminant indicates complex roots, pointing out that the quadratic cannot be factored using real numbers alone.
Polynomial Factorization
Polynomial factorization involves writing a polynomial as the product of its factors, often simplifying complex expressions into more manageable ones. It's comparable to the reverse of expanding products into a polynomial. The main aim is to express the polynomial in such a way that it simplifies understanding or solving equations.For our trinomial \(4x^2 + 20x - 11\), factorization was achieved by determining its roots using the quadratic formula, relying on our prior step while considering integer coefficients. Given roots like \(x = 0.5\) and \(x = -5.5\), it required adjustment for the integer coefficients. Ultimately, through trial and error, it was factorized correctly into:\[(2x - 1)(2x + 11)\]When factored, these expressions provide information and solutions to specific applications like finding length and width of geometric figures. Factorization is a vital skill in algebra, aiding in solving equations and understanding polynomial properties in practical terms.