McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
5. Quadratic Inequalities
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Exercise 38 Page 211

Check if the related quadratic equation has real solutions or not.

Practice makes perfect

To solve the quadratic inequality algebraically, we will follow three steps.

  1. Solve the related quadratic equation.
  2. Plot the solutions on a number line if exist.
  3. Test a value to see if it satisfies the original inequality.

Step 1

We will start by solving the related equation. - 6 = x^2+4x ⇔ - 1x^2+( - 4)x+( - 6)=0 We see above that a= - 1, b= - 4, and c= - 6. Let's substitute these values into the Quadratic Formula to solve the equation.
x=- b±sqrt(b^2-4ac)/2a
x=- ( - 4)±sqrt(( - 4)^2-4( - 1)( - 6))/2( - 1)
Simplify right-hand side
x=4±sqrt((- 4)^2-4(- 1)(- 6))/2(- 1)
x=4±sqrt(16-4(- 1)(- 6))/2(- 1)
x=4±sqrt(16-24)/- 2
x=4±sqrt(- 8)/- 2
We have found a negative discriminant, - 8. Therefore, the related equation has no real solutions.

Step 2

Since the related equation does not have any real solution, we do not have any point to plot on a number line.We have two cases: either all x-values satisfy the original inequalty or no x-value satisfies it.

Step 3

Finally, we must test a value to see if it satisfies the original inequality. Testing one value will help us to determine the solution set. Let's choose a value. For simplicity, we will choose x=0.
- 6 > x^2-x
- 6? > ( 0)^2 -( 0)
Simplify right-hand side
- 6 ? > 0 -0
- 6 ≯ 0 *
Since x=0 did not produce a true statement, no x-value satisfies it. We can now write the solution set. { } or ∅