Introduction to inequalities - pre-algebra lesson
What are inequalities? They are just like equations, except that instead of an equals sign, we have one of these signs: less than, greater than, less than or equal, or greater than or equal.
Inequalities usually have lots of solutions so it's not practical to list them. I show how to PLOT the solution set of an inequality on the number line.
Then I talk about WHY we are allowed to add the same number to both sides of an inequality, or subtract the same number from both sides of an inequality, and it still holds true.
Lastly we solve some simple linear inequalities by adding or subtracting. The 2nd part of this lesson deals with inequalities where we multiply or divide the inequality by the same (positive) number.
In the second video, I first justify the reason WHY we are allowed to multiply or divide an inequality by a positive number without the inequality sign changing, and then secondly I solve a variety of simple linear inequalities. It is meant for pre-algebra students. I don't deal with the situation where the number we multiply or divide by is negative, because this lesson matches Math Mammoth Grade 7 curriculum, where that topic is not covered.
See also
Graphing equations — video lesson
Math Mammoth Grade 7 curriculum (pre-algebra)