Inequalities that Allow Equality
Okay, time out. How can you be an inequality and allow equality? Isn't that an oxymoron? Can you also perform an injustice that is just? Or have indigestion while digesting?
The answer is that some inequalities are not entirely unequal: there's an overlap. The inequalities we've already worked with—the ones involving the symbols "<" and ">"—are called strict inequalities, because the variable isn't allowed to equal the number to which it's being compared. If x < 3, then x can be 2.9, 2.99, 2.999, and so on, but x can't equal 3.
However, we can also write inequalities involving the symbols "≤" and "≥". The "≤" symbol means "less than or equal to," while "≥" is an abbreviation for "greater than or equal to." The values on each side of the symbol aren't exactly equal, making it an inequality, and yet one of the possible solutions does equal the value on the opposite side, therefore making it slightly equal. Got that?
- "Two is less than or equal to x" can be written in symbols as 2 ≤ x. In other words, x must be at least 2.
- We can abbreviate "x is less than or equal to -1" as x ≤ -1.
- The inequality 4 ≥ y means "4 is greater than or equal to y". In other words, y is at most 4.
The inequalities "≤" and "≥" allow the variable to equal the number to which it's being compared. These guys are known in the math world as non-strict inequalities. We might also call them "lenient inequalities." Hey, that's actually good. That might catch on.
Since "≤" and "≥" allow the variable to equal the number to which it's being compared, we can think of them as inequalities that "allow equality," or as "relaxed" inequalities. We like the second one. It makes us think of vacation.
- y = 4 is a solution to the inequality 4 ≥ y.
- x = 5 is a solution to the inequality x ≥ 5.
We still have equivalent ways to write non-strict inequalities.
To represent the inequality 4 ≥ x or the equivalent inequality x ≤ 4, we shade all values up to and including 4.
Be Careful: To represent a strict inequality on a number line, use an empty circle. To represent a non-strict inequality on the number line, use a closed circle or a big filled-in dot. Be careful to draw the right kind of circle and pay close attention to the pictures that you get. If you get a landscape of the Swiss countryside, something has gone awry.