A Simple Inequality Concept That is Giving Me Trouble

[alexac2]

When rearranging an inequality, when do you switch the sign?

eg

x-1<y

Say I want to isolate x can I do this?

x<y+1

[tdadic84]

yes u can...

only switch the sign when u divide my a negative...

[alexac2]

Interesting, thank you.

[austin]

Alex,

-x < 2 => x> -2 (multiply or divide by negative sign on both sides will switch the inequality)

-x> -2 => x<2 (same rule)

-x<-2 => x>2 (same rule)

-x > 2 => x < -2 (same rule)

[logitech]

lets see it with some numbers

-4 < -3

4 > 3


AHA sign changed, when we multiply both side with - 1

Or

3 > -7

-3 < 7

Hmmm

-6 < - 4


- 6 + 40 < - 4 + 40

34 < 36

Sign did not change!!!

-6 - 40 < -4 - 40

-46 < - 44

sign did not change

now lets divide this by +2

-23 < - 22

sign did not change, lets try it with -2

23 > 22

AHA sign changed!!


So whenever you multiply or divide by a negative number make sure to change the sign and remember this exercise!

Have Fun!