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LESSON 1.9 QUADRATIC
INEQUALITIES
Objectives:
At the end of the session, you should be able to:
 Illustrate quadratic inequalities;
 Solve problems involving quadratic inequalities
Recall:
Solving Inequalities:
1. Graph Form
2. Set Form
3. Interval Form
Recall:
Solving Inequalities:
1. Graph Form
2. Set Form
3. Interval Form
Recall:
Quadratic Inequalities
A quadratic inequality is an inequality of the form:
π‘Ž π‘₯2
+𝑏π‘₯+𝑐 <0 π‘Ž π‘₯2
+𝑏π‘₯+𝑐 ≀ 0
π‘Ž π‘₯2
+𝑏π‘₯+𝑐 >0 π‘Ž π‘₯2
+𝑏π‘₯+𝑐 β‰₯ 0
Where a, b and c are real numbers with .
If a quadratic inequality is factorable, it can be solved using a sign graph. A
sign graph shows where each factor is positive, negative or zero.
Summary: Solving Quadratic Inequalities
Given and
Then, the condition of the quadratic inequalities are the following:
𝒂 π’™πŸ
+𝒃𝒙+𝒄>𝟎 Solution:
𝒂 π’™πŸ
+𝒃𝒙+𝒄 β‰₯ 𝟎 Solution:
𝒂 π’™πŸ
+𝒃𝒙+𝒄<𝟎 Solution:
𝒂 π’™πŸ
+𝒃𝒙+𝒄 ≀ 𝟎 Solution:
Solve Quadratic Inequalities π’™πŸ
βˆ’πŸ“ 𝒙 +πŸ’>𝟎
𝒂 π’™πŸ
+𝒃𝒙+𝒄>𝟎 Solution:
Solve Quadratic Inequalities π’™πŸ
+πŸ‘π’™ βˆ’πŸ’β‰₯ 𝟎
𝒂 π’™πŸ
+𝒃𝒙+𝒄 β‰₯ 𝟎 Solution:
Solve Quadratic Inequalities 𝟐 π’™πŸ
+𝒙 βˆ’πŸ”<𝟎
𝒂 π’™πŸ
+𝒃𝒙+𝒄<𝟎 Solution:
Solve Quadratic Inequalities π’™πŸ
βˆ’πŸ’ 𝒙 βˆ’πŸπŸβ‰€ 𝟎
𝒂 π’™πŸ
+𝒃𝒙+𝒄 ≀ 𝟎 Solution:
Quadratic Inequalities
Solve:
1. Write the standard form of the equation:
Find the critical points of the inequality by equating each factor to zero, then solve for the
unknown:
π‘₯2
βˆ’3 π‘₯ β‰₯βˆ’ 2
π‘₯2
βˆ’3 π‘₯+2β‰₯ 0
2. Factored form of quadratic equation: (π‘₯βˆ’ 2)(π‘₯ βˆ’1)β‰₯ 0
Method 1
Quadratic Inequalities
Construct a table listing the factors, the
product, and interval covering the whole
real number line.
- + +
- - +
+ - +
Since , we look at the column of the interval where the product is positive. Hence, the solution
is
Quadratic Inequalities using sign graph
Solve: π‘₯2
βˆ’3 π‘₯+2 β‰₯ 0
0 1 2
Method 2 – Sign Graph
π‘₯2
βˆ’3 π‘₯+2 β‰₯ 0
(π‘₯βˆ’ 2)(π‘₯ βˆ’1)β‰₯ 0
Quadratic Inequalities using sign graph
Solve: π‘₯2
+3 π‘₯ <0
0 1 2
Method 2 – Sign Graph
Quadratic Inequalities using sign graph
Solve: π‘₯2
+π‘₯ βˆ’6>0
Method 2 – Sign Graph
0 1 2
0 1 2
Quadratic Inequalities using sign graph
Solve: π‘₯2
≀ 2 π‘₯ +8
0 1 2
Method 2 – Sign Graph