Key Concepts of Graphing Linear Inequalities to Know for Intermediate Algebra

Graphing linear inequalities helps visualize relationships between variables. By understanding symbols like <, ≤, >, and ≥, you can identify boundary lines and shade regions that represent solutions, making it easier to solve real-world problems involving constraints.

1. Understand the difference between < and ≤, > and ≥

   • "<" means "less than" and does not include the boundary.
   • "≤" means "less than or equal to" and includes the boundary.
   • ">" means "greater than" and does not include the boundary.
   • "≥" means "greater than or equal to" and includes the boundary.

2. Identify the boundary line (y = mx + b)

   • The equation of the line is in slope-intercept form: y = mx + b.
   • "m" represents the slope, indicating the steepness of the line.
   • "b" represents the y-intercept, where the line crosses the y-axis.

3. Determine if the boundary line is solid or dashed

   • A solid line is used for ≤ or ≥, indicating that points on the line are included in the solution.
   • A dashed line is used for < or >, indicating that points on the line are not included in the solution.

4. Test a point to determine which side of the line to shade

   • Choose a test point not on the boundary line (commonly (0,0) if it’s not on the line).
   • Substitute the test point into the inequality to see if it makes the inequality true or false.
   • If true, shade the region containing the test point; if false, shade the opposite side.

5. Shade the correct region of the graph

   • Shading indicates all the solutions to the inequality.
   • Ensure the shaded area reflects the direction indicated by the inequality symbol.
   • The shaded region represents all points (x, y) that satisfy the inequality.

6. Graph vertical and horizontal lines (x = a, y = b)

   • A vertical line (x = a) is drawn straight up and down at x = a.
   • A horizontal line (y = b) is drawn straight across at y = b.
   • These lines represent inequalities that restrict one variable while allowing the other to vary.

7. Recognize and graph compound inequalities

   • Compound inequalities involve two or more inequalities combined, often using "and" or "or."
   • "And" means the solution must satisfy both inequalities simultaneously.
   • "Or" means the solution can satisfy either inequality.

8. Interpret the meaning of the shaded region

   • The shaded region represents all possible solutions to the inequality.
   • Each point in the shaded area is a solution that satisfies the inequality.
   • Understanding the context of the problem can help interpret what the shaded area represents in real-world scenarios.

9. Solve systems of linear inequalities

   • A system consists of two or more inequalities that must be satisfied simultaneously.
   • Graph each inequality on the same coordinate plane.
   • The solution set is the region where the shaded areas of all inequalities overlap.

10. Identify the solution set of an inequality

• The solution set includes all points (x, y) that satisfy the inequality.
• It can be expressed in set notation or graphically represented on a coordinate plane.
• Understanding the solution set helps in solving real-world problems involving constraints.