Chapter 3: Problem 212
If the roots of the equation \(x^{2}-b x+c=0\) be two consecutive integers then \(b^{2}-4 c=\) (a) \(-2\) (b) \(-3\) (c) 3 (d) 1
Short Answer
Expert verified
There is no unique value for \(b^2 - 4c\), as none of the values given in the options will always hold true.
Step by step solution
01
Represent the consecutive integers as roots
Let the consecutive integers be \(n\) and \(n + 1\), where \(n\) is an integer. These integers are the roots of the given quadratic equation.
02
Apply the sum and product properties of quadratic equations
For a quadratic equation of the form \(ax^2 + bx + c = 0\), the sum of the roots is \(-\frac{b}{a}\) and the product of the roots is \(\frac{c}{a}\). In our case, since the equation is \(x^2 - bx + c = 0\), we have \(a = 1\).
So, the sum of the roots is \(-b\) and the product of the roots is \(c\).
03
Set up and solve the system of equations
Let's set up the equations using the sum and product properties with the consecutive integers as roots:
Sum of roots: \(n + (n + 1) = -b\) => \(2n + 1 = -b\)
Product of roots: \(n(n + 1) = c\)
Now, we'll solve the first equation for \(n\) and substitute it into the second equation.
04
Solve for n and calculate c
From the first equation we have \(n = -\frac{b - 1}{2}\). Substituting this into the second equation,
\(-\frac{b - 1}{2}(-\frac{b - 1}{2} + 1) = c\)
Multiplying both sides by 4 to get rid of the fractions,
\((b - 1)(1 - b + 2) = 4c\)
Which becomes:
\((b - 1)(3 - b) = 4c\)
Now we have expressions for both b and c in terms of n. Next, we'll find an expression for \(b^2 - 4c\) and simplify.
05
Calculate b^2 - 4c and simplify
We'll substitute the expressions for b and c from the previous steps:
\([2n + 1]^2 - 4[(b - 1)(3 - b)]\)
Expanding and simplifying, we get:
\((4n^2 + 4n + 1) - 4(3b - b^2 - 2 + b) = (4n^2 + 4n + 1) - 4(4b - b^2 - 1)\)
Continuing to simplify,
\(4n^2 + 4n + 1 - 16b + 4b^2 + 4 = 4b^2 - 16b + 4n^2 + 4n + 5\)
So we have:
\(b^2 - 4c = 4n^2 + 4n + 5\)
Since there are no restrictions given on the possible values of n, there is no unique value for \(b^2 - 4c\). Therefore, there is no correct answer amongst the choices provided, as none of the values given in the options will always hold true.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Sum and Product of Roots
Understanding the relationship between the roots of a quadratic equation and its coefficients is a fundamental aspect of algebra. This relationship is particularly embodied in the sum and product of roots. For the general quadratic equation in the standard form, \(ax^2 + bx + c = 0\), the sum of the roots \(\text{(\text{root}_1 + \text{root}_2)}\) can be found using \(-\frac{b}{a}\), and the product \(\text{(\text{root}_1 \times \text{root}_2)}\) is \(\frac{c}{a}\).
This stems from the fact that if \(\text{root}_1\) and \(\text{root}_2\) are the roots of the equation, then \(x^2 - (\text{root}_1 + \text{root}_2)x + \text{root}_1 \times \text{root}_2 = 0\) can be constructed, which simplifies to the above relationship when compared to the standard form. This concept is widely used to solve problems involving quadratic equations, especially when the roots have certain properties or relationships, such as being consecutive integers, as in the given textbook exercise.
This stems from the fact that if \(\text{root}_1\) and \(\text{root}_2\) are the roots of the equation, then \(x^2 - (\text{root}_1 + \text{root}_2)x + \text{root}_1 \times \text{root}_2 = 0\) can be constructed, which simplifies to the above relationship when compared to the standard form. This concept is widely used to solve problems involving quadratic equations, especially when the roots have certain properties or relationships, such as being consecutive integers, as in the given textbook exercise.
Quadratic Equation
A quadratic equation is an algebraic expression of the second degree, typically in the form of \(ax^2 + bx + c = 0\), where \(a\), \(b\), and \(c\) are constants, and \(x\) represents an unknown variable. The graph of a quadratic function is a parabola that opens upward if \(a > 0\) and downward if \(a < 0\).
The values of \(x\) that satisfy the quadratic equation are known as the roots. These can be real or complex numbers and are found through factoring, completing the square, or utilizing the quadratic formula, \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\). The expression under the square root, \(b^2 - 4ac\), is known as the discriminant and provides vital information about the nature of the roots. A positive discriminant indicates two distinct real roots, zero means one real root (repeated), and a negative discriminant suggests two complex roots.
The values of \(x\) that satisfy the quadratic equation are known as the roots. These can be real or complex numbers and are found through factoring, completing the square, or utilizing the quadratic formula, \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\). The expression under the square root, \(b^2 - 4ac\), is known as the discriminant and provides vital information about the nature of the roots. A positive discriminant indicates two distinct real roots, zero means one real root (repeated), and a negative discriminant suggests two complex roots.
Algebraic Expressions
Algebraic expressions are combinations of numbers, variables, and operations such as addition, subtraction, multiplication, and division. They are the building blocks of algebra and allow us to represent real-life quantities and their relationships abstractly. Expressions can be as simple as \(5x\) or as complex as \((x^2 + 3x + 2)/(x - 1)\).
The manipulation of these expressions according to algebraic principles is what enables us to solve equations. For our quadratic scenarios, expressing roots as consecutive integers leads us to set up systems of equations which when solved, help reveal more about the structure of the quadratic equation itself. Algebraic expressions can be factored, expanded, and simplified to uncover the value of the unknown variable or to compare against other equations for solutions.
The manipulation of these expressions according to algebraic principles is what enables us to solve equations. For our quadratic scenarios, expressing roots as consecutive integers leads us to set up systems of equations which when solved, help reveal more about the structure of the quadratic equation itself. Algebraic expressions can be factored, expanded, and simplified to uncover the value of the unknown variable or to compare against other equations for solutions.