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  Discussion about math, puzzles, games and fun.   Useful symbols: √ ∞ ≠ ≤ ≥ ≈ ⇒ ∈ Δ θ ∴ ∑ ∫ π -




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Topic review (newest first)

2012-11-16 10:20:12

Wow, this is incredible. Thank you really. I don't know why people don't get taught stuff like this sometimes, or maybe I forgot, but never the underlying reasons for the rules it seems. This actually makes sense. Thank you. I don't think I will forget it again. I drew it out with three examples!! big_smile

bob bundy
2012-11-16 09:15:14


Take a look at the diagram

On the right I am trying to show that 3 < 9

When you multiply or divide by -1 it becomes   -9 < -3

Make up your own example.  When you multiply or divide by a negative it has the effect of reflecting in the 'y axis' so the inequality flips around.

Hope that makes sense.


bob bundy
2012-11-16 09:09:06

Definitely a reason.  Maths is like that !!!!!

Explanation coming up


2012-11-16 09:06:04

Thank you very very much indeed. The change of the inequality sign is what got me. Thank you for helping me.

This makes sense. With this rule though, I just must remember it, right? Does it exist for a reason? Or is it just one we must remember?


bob bundy
2012-11-16 08:56:54

hi BarandaMan

x by 5

Add 2z

take 6

divide by 2

I suspect you ran into difficulty because of this

take 2

divide by -2

when you multiply or divide by a negative amount you must reverse the inequality sign


If you want to explore this rule some more, post back.

hi bobbym, sorry didn't know you were posting too.

2012-11-16 08:54:09


Can you please show me your working?

2012-11-16 08:50:59

Hi BarandaMan;

I am getting z > -2.

2012-11-16 08:40:55

Hope you all are doing good.

I have

(6/5) > (2/5) - (2/5)z

I get this down to z > 2.

The answer says it should be, z < 2.

Please help me? Thank you!!!!

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