Solve the Quadratic Inequality: x²-6x+8 Greater Than Zero

Quadratic Inequalities with Factoring Method

Solve the following equation:

x26x+8>0 x^2-6x+8>0

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1

Understand the problem

Solve the following equation:

x26x+8>0 x^2-6x+8>0

2

Step-by-step solution

Let's solve the inequality x26x+8>0 x^2 - 6x + 8 > 0 by breaking it down into steps:

**Step 1: Find the Roots of the Equation**
To solve the inequality, we first need to find the solutions to the equation x26x+8=0 x^2 - 6x + 8 = 0 . This can be done by factoring or using the quadratic formula.

Let's factor the quadratic expression:
x26x+8=(x2)(x4) x^2 - 6x + 8 = (x - 2)(x - 4)

The roots of the equation are x=2 x = 2 and x=4 x = 4 .

**Step 2: Test Intervals**
The roots divide the number line into three intervals: (,2) (-\infty, 2) , (2,4) (2, 4) , and (4,) (4, \infty) . We need to test each of these intervals to see where the inequality holds.

  • For x(,2) x \in (-\infty, 2) , choose x=0 x = 0 :
    (02)(04)=8 (0 - 2)(0 - 4) = 8 , which is positive, so x26x+8>0 x^2 - 6x + 8 > 0 .
  • For x(2,4) x \in (2, 4) , choose x=3 x = 3 :
    (32)(34)=1 (3 - 2)(3 - 4) = -1 , which is negative, so x26x+8<0 x^2 - 6x + 8 < 0 .
  • For x(4,) x \in (4, \infty) , choose x=5 x = 5 :
    (52)(54)=3 (5 - 2)(5 - 4) = 3 , which is positive, so x26x+8>0 x^2 - 6x + 8 > 0 .

**Conclusion**:
The inequality is satisfied for x<2 x < 2 and x>4 x > 4 .

Thus, the solution to the inequality x26x+8>0 x^2 - 6x + 8 > 0 is x<2 x < 2 or x>4 x > 4 .

The correct choice is x<2,4<x x < 2,4 < x .

3

Final Answer

x<2,4<x x < 2,4 < x

Key Points to Remember

Essential concepts to master this topic
  • Factoring: Convert x26x+8=0 x^2 - 6x + 8 = 0 to (x2)(x4)=0 (x-2)(x-4) = 0
  • Interval Testing: Test x = 0: (02)(04)=8>0 (0-2)(0-4) = 8 > 0
  • Check: Verify solution by testing values in each interval ✓

Common Mistakes

Avoid these frequent errors
  • Solving x² - 6x + 8 = 0 instead of > 0
    Don't just find where the quadratic equals zero and stop there = missing the actual solution! The inequality asks where the expression is positive, not zero. Always test intervals between the roots to find where the inequality holds.

Practice Quiz

Test your knowledge with interactive questions

Solve the following equation:

\( x^2+4>0 \)

FAQ

Everything you need to know about this question

Why do I need to find the roots first if the inequality uses > instead of =?

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The roots are boundary points that divide the number line into intervals. Once you know where the quadratic equals zero, you can test each interval to see where it's positive or negative!

How do I know which intervals to test?

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The roots x=2 x = 2 and x=4 x = 4 create three intervals: before 2, between 2 and 4, and after 4. Pick any test point in each interval.

Why is the answer x < 2 or x > 4 instead of 2 < x < 4?

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When we tested x=3 x = 3 (between the roots), we got negative result. The inequality wants positive values, so the solution is the intervals where our tests were positive!

Can I use the quadratic formula instead of factoring?

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Yes! The quadratic formula will give you the same roots: x=2 x = 2 and x=4 x = 4 . But you still need to test intervals to solve the inequality.

What does the notation x < 2, 4 < x mean?

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This means x is less than 2 OR x is greater than 4. It's the same as writing (,2)(4,) (-\infty, 2) \cup (4, \infty) in interval notation.

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