Solve the Quadratic Inequality: x²-8x+12>0 Step by Step

Quadratic Inequalities with Factoring Method

Solve the following equation:

x28x+12>0 x^2-8x+12>0

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1

Understand the problem

Solve the following equation:

x28x+12>0 x^2-8x+12>0

2

Step-by-step solution

Let's proceed to solve the inequality x28x+12>0 x^2 - 8x + 12 > 0 .

  • Start by factoring the quadratic: x28x+12 x^2 - 8x + 12 .
  • Identify the factors of 12 that sum to 8: 6 6 and 2 2 . This results in: (x6)(x2)=0 (x - 6)(x - 2) = 0 .

The factorization gives us the critical points x=6 x = 6 and x=2 x = 2 . These points divide the number line into three intervals: x<2 x < 2 , 2<x<6 2 < x < 6 , and x>6 x > 6 .

Now, we evaluate the sign of the product (x6)(x2) (x - 6)(x - 2) in each interval:

  • For x<2 x < 2 : Both (x6) (x - 6) and (x2) (x - 2) are negative, so their product is positive.
  • For 2<x<6 2 < x < 6 : (x2) (x - 2) is positive, (x6) (x - 6) is negative, so their product is negative.
  • For x>6 x > 6 : Both (x6) (x - 6) and (x2) (x - 2) are positive, so their product is positive.

The inequality (x6)(x2)>0 (x - 6)(x - 2) > 0 holds for x<2 x < 2 and x>6 x > 6 .

Thus, the solution to the inequality x28x+12>0 x^2 - 8x + 12 > 0 is x<2 x < 2 or x>6 x > 6 .

Therefore, the correct answer is x<2,6<x \boxed{x < 2, 6 < x} .

3

Final Answer

x<2,6<x x < 2,6 < x

Key Points to Remember

Essential concepts to master this topic
  • Rule: Factor the quadratic first to find critical points
  • Technique: Test signs in intervals: (x2)(x6)>0 (x-2)(x-6) > 0
  • Check: Verify with test values: x = 0 gives positive, x = 4 gives negative ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to check signs in all intervals
    Don't just find the critical points x = 2 and x = 6 and stop = wrong solution! This misses which intervals make the inequality true. Always test the sign of the expression in each interval created by the critical points.

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 we factor the quadratic first?

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Factoring reveals the critical points where the expression equals zero! These points x=2 x = 2 and x=6 x = 6 divide the number line into regions where the expression is either positive or negative.

How do I know which intervals to include in my answer?

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Test a value from each interval in the factored form (x2)(x6) (x-2)(x-6) . Since we want greater than zero, include intervals where your test gives a positive result.

What's the difference between > and ≥ in the solution?

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With >, we exclude the critical points where the expression equals zero. With , we would include them. Since x28x+12>0 x^2-8x+12 > 0 , our answer is x<2 x < 2 or x>6 x > 6 .

Can I solve this without factoring?

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You could use the quadratic formula to find the roots, but factoring is faster when possible! The critical points are the same either way: where the quadratic equals zero.

How do I write the final answer correctly?

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Use interval notation (,2)(6,) (-∞, 2) \cup (6, ∞) or inequality notation x<2 x < 2 or x>6 x > 6 . Both mean the same thing!

What if I can't factor the quadratic?

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Use the quadratic formula to find the roots, then proceed with the same sign analysis method. The process is identical, just with decimal critical points!

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