What I have learned about grade 9 math inequalities

What is an inequality?

an inequality is a math question using these symbols: <, >, ≤, ≥

what do these symbols mean?

< = less than

> = greater than

≤ = less than or equal to

≥ = greater than or equal to

unlike normal math equations inequalities can have infinite answers.

ex: 4>x

x can be 3, 2, 1, 0, -1….

now that we got that out of the way; inequalities can be just like normal math equations!!! (with some exceptions)

ex: 2x \div3-5 ≤ 2x+2

(2x \div3-5)3 ≤ (2x+2)3

2x-15 ≤ 6x+6

2x-2x-15 ≤ 6x-2x+6

-15 ≤ 4x+6

-15-6 ≤ 4x+6-6

-21 ≤ 4x

-5.25 ≤ x

or x ≥ -5.25

which means any number that is -5.25 or bigger could be the answer.

to check that’s true we can replace x by 6 to see if we get a true statement.

2 \cdot6 \div3-5 ≤ 2 \cdot6+2

12 \div3-5 ≤ 12+2

4-5 ≤ 14

-1 ≤ 14

and as we can see here -1 is in fact smaller than 14 which means we did our work right. we can also check the equal sign to see if we really did the work right by replacing x by -5.25 and seeing if we get an equivalent equation when we solve it.

2 \cdot-5.25 \div3-5 = 2 \cdot-5.25+2

-10.5 \div3-5 = -10.5+2

-3.5-5 = -10.5+2

-8.5 = -8.5

and as we can see here -8.5 is equivalent to -8.5 which means we did a perfect job on this equation.

Exceptions

there is 1 exception when working with inequalities and that is when multiplying both sides by a negative when you do that you need to flip the symbol for example > turns into < also when you have an equation like 4 < x and you want to make it x > 4 you need to flip the symbol.


How to put inequalities on a number line 

To put inequalities on a number line its easy for example if you have -2 < x then you would get

its that easy

but you need to watch out for these symbols: ≤ and ≥

for these symbols you need to do the same thing but instead of leaving an open dot you make a solid dot. If its a solide dot that means that that number and bigger/smaller is the answer is you leave it an ope dot than that means that the answer is bigger/smaller then that number not including that number.

ex: -5 ≤ x

now you might run into stuff to model like this 0 < x ≤ 4 dont worry that just means your going to have to have the answer in-between 0 and 4. To put in on a number line you need to make the line from 0 to 4 without arrows and have them connect at both dots like this.

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