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

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Topic review (newest first)

BarandaMan
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

OK.

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

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

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

Explanation coming up

Bob

BarandaMan
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?

Thanks!!!!

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



Bob

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

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

BarandaMan
2012-11-16 08:54:09

Really?!

Can you please show me your working?

bobbym
2012-11-16 08:50:59

Hi BarandaMan;

I am getting z > -2.

BarandaMan
2012-11-16 08:40:55

Hey!
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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