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

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Topic review (newest first)

bobbym
2012-08-01 04:15:45

There is also one more reason to check.

anonimnystefy
2012-08-01 03:49:25

The concept of negative length I think already exists, but not in regular geometry.

bob bundy
2012-08-01 03:27:17

I agree.  You should always check any answers you get.

Consider this:

A rectangle is 3 cm longer than it is wide.  It has an area of 40 cm^2.

So, let the width be x => the length is x + 3 => the area is x(x + 3)





So answers may appear than are not solutions (unless you want to make a new topic in maths with 'negative lengths'  smile  )

Bob

bobbym
2012-08-01 01:38:26

Does that invalidate the quadratic formula, or completing the square or any other way to get roots? You are always required to check the roots! Also with combinatoric problems too...

Kaboobly doo with the restrictions.

anonimnystefy
2012-08-01 01:34:10

I never said it di have to be easy. i am just saying that there should be another way of checking that doesn't require plugging in, because the solution may not be always pretty and a computer might not always be the when you need it.

The solution has no flaws except that you didn't set any restrictions.

bobbym
2012-08-01 01:26:32

You are missing the point.

1) Why must it be easy to plug in? Does that invalidate the solution?

2) There are some obvious faults with the whole idea and I only presented it when I was sure the OP had already been satisfied.

anonimnystefy
2012-08-01 01:17:07

Hi bobbym

That is based on the simplicity of the solution. If it was something worse, you wouldn't be able to substitute and check easily without a computer.

bob bundy
2012-08-01 00:58:13

-2 is a solution to the equation



It arises because of the method of solution.

Bob

bobbym
2012-08-01 00:25:01

Hi;

But I think you should explain why -2 isn't a solution.

Spurious solutions are detected by plugging in. -2 does not work.

anonimnystefy
2012-07-31 19:25:04

Hi bobbym

Nice one. But I think you should explain why -2 isn't a solution.

bobbym
2012-07-31 12:42:35

Hi;

anonimnystefy
2012-07-30 23:06:18

I never said tachers new everything. It just seems logical. Even our book says it is better if we did itbthat way, so that we are sure both sides are positive.

bob bundy
2012-07-30 22:18:17

hi Stefy







and







I realise it will be hard for you to believe it but, sometimes, even teachers talk a load of rubbish.  smile

aude sapere  smile

Bob

anonimnystefy
2012-07-30 17:49:47

Hi Bob

Of course he said. But I forgot. I think it is so that we make sure neither side is negative.

Hi 295Ja

You're welcome. Hope everything else was okay during the storm.

295Ja
2012-07-30 17:47:11

Hi bob bundy!

An average of 20 storms and/or typhoons per year enters the Philippines usually from July through October.

By the way, I'm now moving on to solving problems about inequalities then 2 dimensional coordinate system.
Glad I could ask problems I can't solve here! smile

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