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

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Topic review (newest first)

NoSash
2006-02-14 10:52:50

Hey guys, apparently it's incorrect to put the absolute value signs, can anybody confirm this? Or support it? I know it works out mathematically but I was told it's still wrong.

NoSash
2006-02-08 03:51:39

yeah it all makes sense, thanks guys

mathsyperson
2006-02-08 03:37:19

All of the above is correct. They've hidden it with lots of unnecessary complications, but what they're basically doing is saying that as x² = (-x)², then x = -x, even though it doesn't.

krassi_holmz
2006-02-07 20:00:30

Yep.

kempos
2006-02-07 19:47:56

step 5. there you should have absolute value.

krassi_holmz
2006-02-07 17:57:01

e.a.
4)                     (4 - 9/2)^2 = (5 - 9/2)^2
5)                            |4-9/2|=|5-9/2|
6)                              |-0.5|=|+0.5|
which is OK.

darthradius
2006-02-07 09:58:00

when you take the square root, you need the which gives you a few different combinations...this "proof" just uses one combination that does not work.

NoSash
2006-02-07 09:48:11

1)                           16 - 36 = 25 - 45
2)                16 - 36 + 81/4 = 25 - 45 + 81/4
3) 4^2 - 2x4x9/2 + (9/2)^2 = 5^2 - 2x5x9/2 + (9/2)^2
4)                     (4 - 9/2)^2 = (5 - 9/2)^2
5)                           4 - 9/2 = 5 - 9/2
6)                                   4 = 5

What went wrong?

I'm pretty sure the error is from step 3 to 4 but I don't know what the heck they are trying to do.

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