Chapter 2: Problem 9
For the following exercises, solve the quadratic equation by factoring. $$ 6 x^{2}+17 x+5=0 $$
Short Answer
Expert verified
The solutions are \(x = -\frac{1}{3}\) and \(x = -\frac{5}{2}\).
Step by step solution
01
Identify the Quadratic Equation
The given quadratic equation is \(6x^2 + 17x + 5 = 0\). It is in the standard form \(ax^2 + bx + c = 0\), where \(a = 6\), \(b = 17\), and \(c = 5\).
02
Find Two Numbers that Multiply to ac and Add to b
Calculate \(ac\), which is \(a \times c = 6 \times 5 = 30\). Find two numbers that multiply to 30 and add to 17. These numbers are 15 and 2, since \(15 \times 2 = 30\) and \(15 + 2 = 17\).
03
Rewrite the Middle Term
Rewrite the quadratic equation using the numbers found in Step 2: \(6x^2 + 15x + 2x + 5 = 0\). This replaces the 17x with 15x and 2x.
04
Factor by Grouping
Group the terms to factor by grouping: \((6x^2 + 15x) + (2x + 5) = 0\).Factor out the greatest common factor from each group: - From \(6x^2 + 15x\), factor out \(3x\) to get \(3x(2x + 5)\).- From \(2x + 5\), factor out 1 to get \(1(2x + 5)\).The equation becomes \(3x(2x + 5) + 1(2x + 5) = 0\).
05
Factor Out the Common Binomial
Recognize the common binomial factor \((2x + 5)\) in both terms: \((3x + 1)(2x + 5) = 0\).
06
Solve for x
Set each factor equal to zero and solve for \(x\): 1. \(3x + 1 = 0\) leads to \(3x = -1\), thus \(x = -\frac{1}{3}\). 2. \(2x + 5 = 0\) leads to \(2x = -5\), thus \(x = -\frac{5}{2}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Factoring
Factoring is a method used to solve quadratic equations by expressing them as a product of simpler polynomials. It's a technique where you find two numbers that satisfy a specific set of conditions. For a quadratic equation of the form \(ax^2 + bx + c = 0\), you look for two numbers that multiply to \(ac\) (the product of the coefficient of \(x^2\) and the constant term) and add up to \(b\) (the coefficient of \(x\)).
- Example: In the quadratic equation \(6x^2 + 17x + 5 = 0\), notice \(a = 6\), \(b = 17\), and \(c = 5\). The product \(ac = 30\). A pair such as 15 and 2 can multiply to 30 and add to 17.
- You then rewrite the middle term, \(17x\), using these numbers to split it into two terms: \(6x^2 + 15x + 2x + 5\).
- Group the first two terms and the last two terms, i.e., \((6x^2 + 15x) + (2x + 5) = 0\), allowing you to factor by grouping.
- Finally, factor each group and then factor out the common binomial, leading you to find \(x\) values that satisfy the original quadratic equation.
Quadratic Formula
The quadratic formula is a universal method used to solve any quadratic equation, regardless of its ability to be factored easily. The formula is derived from completing the square on the general form of a quadratic equation. If your quadratic equation is in the form \(ax^2 + bx + c = 0\), the solutions can be found using:
\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]
\[x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\]
- The term under the square root, \(b^2 - 4ac\), is called the discriminant. It determines the nature of the roots:
- If it is positive, there are two distinct real roots.
- If it is zero, there's exactly one real root or a repeated real root.
- If it is negative, the quadratic equation has no real roots, but has two complex numbers as roots.
- Using our example \(6x^2 + 17x + 5 = 0\), if factoring seems tricky, you can readily apply the quadratic formula to find \(x\).
Standard Form of Quadratic Equation
Quadratic equations are expressed in the standard form \(ax^2 + bx + c = 0\). This structure is essential for identifying the coefficients \(a\), \(b\), and \(c\), which play a key role in solving the equation.
- 'A' is the coefficient of \(x^2\), 'B' is the coefficient of \(x\), and 'C' is the constant term.
- In our exercise, the equation \(6x^2 + 17x + 5 = 0\) is in this standard form with \(a = 6\), \(b = 17\), and \(c = 5\).
- Knowing these coefficients is crucial, whether you're solving the equation by factoring, using the quadratic formula, or other methods.