Chapter 9: Problem 43
Solve by (a) Completing the square (b) Using the quadratic formula $$ 9 x^{2}-6 x+1=0 $$
Short Answer
Expert verified
Question: Solve the quadratic equation $$9x^2 - 6x + 1 = 0$$ using (a) completing the square and (b) the quadratic formula.
Answer: The two solutions obtained using both methods are:
(a) Completing the Square:
$$x_1 = \frac{1}{3} + \frac{i}{3}$$
$$x_2 = \frac{1}{3} - \frac{i}{3}$$
(b) Quadratic Formula:
$$x = \frac{1}{3}$$
Step by step solution
01
(Method A: Completing the Square)
For method A, we will perform the following steps:
1. Write the equation in the standard quadratic form
2. Make the leading coefficient (coefficient of the $$x^2$$ term) equal to 1
3. Add and subtract a constant within the parentheses to complete the square
4. Factor the perfect square trinomial
5. Solve for x using square root property
Step 1: Write the equation in the standard quadratic form
The given equation is already in the standard quadratic form:
$$
9x^2 - 6x + 1 = 0
$$
Step 2: Make the leading coefficient equal to 1
Divide the entire equation by 9:
$$
x^2 - \frac{2}{3}x + \frac{1}{9} = 0
$$
Step 3: Add and subtract the constant within parentheses to complete the square
Add and subtract $$\left(\frac{\frac{2}{3}}{2}\right)^2 = \left(\frac{1}{3}\right)^2 = \frac{1}{9}$$ inside the parentheses.
$$
x^2 - \frac{2}{3}x + \frac{1}{9} - \frac{1}{9} = -\frac{1}{9}
$$
Step 4: Factor the perfect square trinomial
Factor the left side of the equation:
$$
(x-\frac{1}{3})^2 = -\frac{1}{9}
$$
Step 5: Solve for x using square root property
Apply the square root property to both sides:
$$
x - \frac{1}{3} = \pm \sqrt{-\frac{1}{9}}
$$
Then, isolate x:
$$
x = \frac{1}{3} \pm \sqrt{-\frac{1}{9}}
$$
Hence, the two solutions are:
$$
x_1 = \frac{1}{3} + \frac{i}{3}
$$
and
$$
x_2 = \frac{1}{3} - \frac{i}{3}
$$
02
(Method B: Quadratic Formula)
For method B, we will perform the following steps:
1. Identify the coefficients of the quadratic equation
2. Substitute the coefficients into the quadratic formula
3. Simplify to get the solutions of the equation
Step 1: Identify the coefficients of the quadratic equation
The given equation is of the form $$ax^2+bx+c=0$$, and the coefficients are:
$$
a = 9 \\
b = -6 \\
c = 1
$$
Step 2: Substitute the coefficients into the quadratic formula
The quadratic formula is given by:
$$
x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}
$$
Substitute the values of a, b, and c into the formula:
$$
x = \frac{-(-6) \pm \sqrt{(-6)^2 - 4 \cdot 9 \cdot 1}}{2 \cdot 9}
$$
Step 3: Simplify to get the solutions of the equation
Simplify the expression to find the solutions:
$$
x = \frac{6 \pm \sqrt{36 - 36}}{18}
$$
This simplifies to:
$$
x = \frac{6 \pm \sqrt{0}}{18} = \frac{6 \pm 0}{18} = \frac{6}{18} = \frac{1}{3}
$$
Since there is no nonzero value inside the square root, the equation has only one real solution:
$$
x = \frac{1}{3}
$$
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
quadratic equation
A quadratic equation is a second-degree polynomial equation of the form \( ax^2 + bx + c = 0 \), where \( x \) represents an unknown variable, and \( a \), \( b \), and \( c \) are constants with \( a eq 0 \). The quadratic equation is fundamental in mathematics as it describes many natural phenomena and practical situations.
Quadratic equations can be solved using several methods, including:
Quadratic equations can be solved using several methods, including:
- Factoring: Expressing the equation as a product of its roots, if easily factorable.
- Completing the square: Rewriting the equation in a perfect square form.
- Quadratic formula: Applying the formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \) to find the roots.
quadratic formula
The quadratic formula is a powerful tool used to find the solutions, or roots, of any quadratic equation. The formula is expressed as \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), derived from the process of completing the square.
To use the quadratic formula:
To use the quadratic formula:
- Identify the coefficients \( a \), \( b \), and \( c \) from the quadratic equation \( ax^2 + bx + c = 0 \)
- Substitute these values into the quadratic formula
- Simplify the expression under the square root, known as the discriminant, \( b^2 - 4ac \)
- Evaluate the solutions, considering both the positive and negative square root values
- If \( b^2 - 4ac > 0 \), there are two distinct real solutions.
- If \( b^2 - 4ac = 0 \), there is one real solution, often called a repeated or double root.
- If \( b^2 - 4ac < 0 \), the solutions are complex numbers.
complex numbers
Complex numbers are numbers that encompass both a real and an imaginary component. They are expressed in the form \( a + bi \), where \( a \) is the real part, \( b \) is the imaginary part, and \( i \) is the imaginary unit defined as \( i = \sqrt{-1} \). Complex numbers allow mathematicians and engineers to handle equations that don't have real solutions.
Key characteristics of complex numbers include:
Key characteristics of complex numbers include:
- Imaginary unit \( i \): Defined such that \( i^2 = -1 \), helping to solve roots of negative numbers.
- Complex plane: A two-dimensional plane used to graph complex numbers, with the horizontal axis representing the real part and the vertical axis the imaginary part.
- Conjugates: The complex conjugate of \( a + bi \) is \( a - bi \); it is useful in various operations and solving equations.