Chapter 6: Problem 101
Solve each equation. $$ d(8 d-9)=-1 $$
Short Answer
Expert verified
The solutions are \(d = 1\) and \(d = \frac{1}{8}\).
Step by step solution
01
Expand the Equation
First, we'll expand the equation by distributing the term outside the parentheses:\[ d(8d - 9) = -1 \]This becomes:\[ 8d^2 - 9d = -1 \]
02
Set the Equation to Standard Form
Next, we will rearrange the equation to set it into the standard form of a quadratic equation:\[ 8d^2 - 9d + 1 = 0 \]
03
Use the Quadratic Formula
The quadratic formula is given by:\[ d = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]For this equation, \( a = 8 \), \( b = -9 \), and \( c = 1 \). Plug in these values:\[ d = \frac{-(-9) \pm \sqrt{(-9)^2 - 4 \times 8 \times 1}}{2 \times 8} \]
04
Calculate the Discriminant
Calculate the discriminant \( b^2 - 4ac \):\[ (-9)^2 - 4 \times 8 \times 1 = 81 - 32 = 49 \]
05
Solve for d using the Quadratic Formula
Substitute the discriminant back into the quadratic formula:\[ d = \frac{9 \pm \sqrt{49}}{16} \]\[ d = \frac{9 \pm 7}{16} \]Thus, solving gives two solutions:\( d = \frac{16}{16} = 1 \) and \( d = \frac{2}{16} = \frac{1}{8} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Quadratic Formula
A quadratic equation is characterized by its highest exponent being 2 and usually appears in the form \( ax^2 + bx + c = 0 \). The quadratic formula is a powerful tool used to find the solutions of such equations. It is expressed as:\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \]Here's what each part means:
- \( a \) refers to the coefficient of the \( x^2 \) term.
- \( b \) refers to the coefficient of the \( x \) term.
- \( c \) is the constant term.
- Rewrite the equation in the standard form: \( ax^2 + bx + c = 0 \).
- Identify the coefficients \( a \), \( b \), and \( c \).
- Substitute these coefficients into the quadratic formula.
- Solve for \( x \) using the values obtained from the formula.
Discriminant
The discriminant is a vital concept in understanding the nature of solutions for a quadratic equation. It is the part under the square root in the quadratic formula, given by:\[\Delta = b^2 - 4ac\]The discriminant helps determine the number and type of solutions:
- If \( \Delta > 0 \), there are two distinct real solutions.
- If \( \Delta = 0 \), there is exactly one real solution, a repeated root.
- If \( \Delta < 0 \), there are no real solutions; instead, there are two complex solutions.
Standard Form of a Quadratic Equation
Getting a quadratic equation into its standard form is the first step to utilizing tools like the quadratic formula. The standard form is:\[ ax^2 + bx + c = 0 \]The equation needs:
- \( ax^2 \): the term with the squared variable.
- \( bx \): the linear term.
- \( c \): the constant term.