x²-3x-18

Algebra and Trigonometry (6th Edition)
6th Edition
ISBN:9780134463216
Author:Robert F. Blitzer
Publisher:Robert F. Blitzer
ChapterP: Prerequisites: Fundamental Concepts Of Algebra
Section: Chapter Questions
Problem 1MCCP: In Exercises 1-25, simplify the given expression or perform the indicated operation (and simplify,...
Question
### Solving Quadratic Equations: Guess and Check Method

**Equation:**  
\[ x^2 - 3x - 18 \]

**Method: Guess and Check**

### Explanation:

To solve the quadratic equation using the guess and check method, you try to find two numbers that multiply to give -18 and add to give -3. This is useful for factoring quadratics that aren't easily simplified.

**Steps:**

1. **Identify coefficients:** 
   - The equation is in the form \( ax^2 + bx + c \).
   - Here, \( a = 1 \), \( b = -3 \), \( c = -18 \).

2. **Find two numbers:**
   - Look for two numbers that multiply to \( ac = 1 \times -18 = -18 \), and add up to \( b = -3 \).

3. **Test possible pairs:**
   - Possible pairs for multiplication are:
     - (-6, 3)
     - (6, -3)
     - (-9, 2)
     - (9, -2)
   - Among these, (-6, 3) satisfies both multiplying to -18 and adding to -3.

4. **Form factor pairs:**
   - Using the pair (-6, 3), rewrite the middle term:
     - \( x^2 - 6x + 3x - 18 \)
   - Factor by grouping:
     - \( x(x - 6) + 3(x - 6) \)
   - Factor out the common term:
     - \( (x + 3)(x - 6) \)

5. **Solve for \( x \):**
   - Set each factor to zero:
     - \( x + 3 = 0 \) or \( x - 6 = 0 \)
   - Solutions are:
     - \( x = -3 \) or \( x = 6 \)

In this method, guessing and checking different pairs helps find the solutions to the quadratic equation by transforming it into simpler linear equations.
Transcribed Image Text:### Solving Quadratic Equations: Guess and Check Method **Equation:** \[ x^2 - 3x - 18 \] **Method: Guess and Check** ### Explanation: To solve the quadratic equation using the guess and check method, you try to find two numbers that multiply to give -18 and add to give -3. This is useful for factoring quadratics that aren't easily simplified. **Steps:** 1. **Identify coefficients:** - The equation is in the form \( ax^2 + bx + c \). - Here, \( a = 1 \), \( b = -3 \), \( c = -18 \). 2. **Find two numbers:** - Look for two numbers that multiply to \( ac = 1 \times -18 = -18 \), and add up to \( b = -3 \). 3. **Test possible pairs:** - Possible pairs for multiplication are: - (-6, 3) - (6, -3) - (-9, 2) - (9, -2) - Among these, (-6, 3) satisfies both multiplying to -18 and adding to -3. 4. **Form factor pairs:** - Using the pair (-6, 3), rewrite the middle term: - \( x^2 - 6x + 3x - 18 \) - Factor by grouping: - \( x(x - 6) + 3(x - 6) \) - Factor out the common term: - \( (x + 3)(x - 6) \) 5. **Solve for \( x \):** - Set each factor to zero: - \( x + 3 = 0 \) or \( x - 6 = 0 \) - Solutions are: - \( x = -3 \) or \( x = 6 \) In this method, guessing and checking different pairs helps find the solutions to the quadratic equation by transforming it into simpler linear equations.
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