Question

We are learning inequalities and I just did some homework but the teacher returned it saying I did some of them wrong.
1. -2x - 10 < 2
2. -2x + 15 < 17
I didn't flip the inequality sign when I divided by (-2).
But why do we always have to flip the sign when we multiply or divide by a negative number?

Answer 1

In google type:
inequalities and negative numbers

You will find couple sites.
mathforum is good.


1.

-2 x - 10 < 2

-2 x < 2 + 10

-2 x < 12 Divide both sides with -2

x > 12 / - 2

x > - 6


2.

-2x + 15 < 17

-2 x < 17 - 15

-2 x < 2 Divide both sides with -2

x > 2 / -2

x > -1