I thought math was always logical?

[beowulf 1]

Your question doesn't make sense. I don't understand what you are asking.

10x = 3.99 is not related or have anything to do with
10x - x = 39.9 - 3.9

They can not be combined.


The .9s going on forever is implied. There is no way for me to type the - over the top of the 9s.

[steveorino 7]

even if you identify X as 3.999 ...?

steveOrino

[justinb138 0]

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Your question doesn't make sense. I don't understand what you are asking.

10x = 3.99 is not related or have anything to do with
10x - x = 39.9 - 3.9

They can not be combined.

So if x = 3.9..., then 10x cannot be represented by 39.9...

[beowulf 1]

That is a misread on your part. x was not predefined. Your kid solved the equations for X and then put a box around each answer. Two equations two answers.


My math background goes as far as College Calculus 3. Algebra is very easy and I remember seeing things like this.

Ask you kid what the original problems were.

[steveorino 7]

My kid is a 27 year tattoo artist. He was just asking because he thought the same thing as I now do. Many people think their answer is right and everyone else is wrong. They also insult you when you don't "get it"

steveOrino

[beowulf 1]

Not trying to insult you, just telling you what I see.
You can call me and talk to me if you want. I will PM you my phone number.

It's better that he understands what he is doing then being uncertain.

Algebra is very straight forward. NOT EVERYONE can think that logically. That doesn't mean anything is wrong with them. It just meanst they are better at other things and just don't think that way. Which can be a good thing.

[beowulf 1]

I won't bullshit you. I will say exactly what I mean. Often it doesn't come across well.

If you look beyond the emotions I will help you. I will answer to the best of my ability any math question you or your son have.

[steveorino 7]

I'm not saying you are but look at the answers ...

post #2 says"3.99999999999999999. . . . is basically equal to four"

post # 4 says "Anyway 3.9999... as an infinite series converges on the value 4, which makes it equivalent to 4 in certain respects."

post # 8 says "No. 4.0 - 3.999... = 0.000........000....000......
but 4.111.... - 4.0 = 0.11111...

Not very good at math, are you? "

post #11 says "The problem is that multiplying 3.9... by 10 doesn't give you 39.9...

It gives you 39.9...0.

One number would end in 9, the other would end in a 0. "

post #13 says "It depends on what kind of math you are talking about. Deductive math is very different from inductive math. "

post #16 says "No, it doesn't, because there are an INFINITE number of "9"s in both cases, since infinity+1 = infinity " [then he post a website like Hairyjuan always did]

post #18 you say with a condescending note "Very basic algebra. Math isn't for everyone. "

HILARIOUS how much logic is like religion!!

steveOrino

[beowulf 1]

Please call me so that I can better explain my view on this.

I am not communicating very well with you.

[beowulf 1]

I am sorry I came across condescending. I didn't mean it that way.

[likearock 2]

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And I thought that Speaker's Corner was supposed to be about Guns, Gays, or God.]

math is sounding more and more like a religion to me. The answer depends on who you ask and many say it is semantic game, while others insist they are right and the others are wrong.

The difference is in math, some are actually right in a way that can be proven.

The series of statements you provided all derive from from the first statement:

x = 3.99999... (an infinite number of 9s to the right of the decimal point)

They strictly follow the fundamental axiom of algebra, that if you start with a true equation and add/subtract/multiply/divide both sides of the equation by the same quantity, the result is an equally true equation.

The fact that this results in the apparent paradox that 3.9999... = 4 is no accident. As I said earlier, the two quantities are equal in a certain sense. The link that jerryzflies posted (http://www.newton.dep.anl.gov/newton/askasci/1995/math/MATH070.HTM) explains this concept in more detail.

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Forgot to add .. some will insult you when you don't understand their version.

That's not cool.

[beowulf 1]

Please don't relate my posts to anyone else's. They are not related. Please take my post by themselves.

[justinb138 0]

This make sense?

[champu 1]

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And I thought that Speaker's Corner was supposed to be about Guns, Gays, or God.]

math is sounding more and more like a religion to me. The answer depends on who you ask and many say it is semantic game, while others insist they are right and the others are wrong.

The difference is in math, some are actually right in a way that can be proven.

That's correct... and the rest are wrong in a way that can be proven.

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My math background goes as far as College Calculus 3. Algebra is very easy and I remember seeing things like this.

The crux of this problem is not one of "College Calculus 3" nor of Algebra. A course on Discrete Mathematics / Logic / Set Theory would cover it in much better detail. Rosen wrote a pretty good text on the subject...

...which is apparently now in its sixth edition... ...see this is the kind of crap that's going to make me start feeling old really fast.

[beowulf 1]

btw when I said I have seen things like this it wasn't from the text books or the teachers, but from tutoring algebra and it was from the students not being accurate in there writings.

[jdfreefly 1]

That's nothing...check this out:

Let...

a=1
b=1

That means

a=b

multiply both sides by a
a2 = ab

Subtact b2 from both sides
a2 - b2 = ab - b2
Factor

(a+b)(a-b) = b(a-b)

Divide both sides by (a-b)
*crosses out both (a-b)*

a+b=b

If
a=1 and b=1

Then
1+1=1
2=1

Methane Freefly - got stink?

[shropshire 0]

The last step .... divide by (a-b) is very naughty, as both a & b are 1 then you are dividing by zero .. tut ... tut

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[JackC 0]

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math is sounding more and more like a religion to me. The answer depends on who you ask and many say it is semantic game, while others insist they are right and the others are wrong.

Not really. Maths conforms to a fixed set of logical rules and the answer does not depend on who you ask. If you get two different answers from two different people, at least one of them is wrong.

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Not sure how 3.999999999 ... = 4.
Does 4.1111111 ... equal 4 too?

In this case the proof only works because 3.999... is asymptotically equal to 4. That is the difference bewteen 3.999... and 4 gets closer and closer to zero as you add more 9s and it is implied that there are an infinite number of 9s so the difference is infinitesimally close to zero (read: is equal to zero if the series extends to infinity). The proof is correct but intentionally designed to confuse readers not familiar with the concept of infinite series in maths.

http://en.wikipedia.org/wiki/Geometric_series

[billeisele 130]

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That's nothing...check this out:

Let...

a=1
b=1

That means

a=b

multiply both sides by a
a2 = ab

----------------
not where I come from
a2 = 2
ab = 1

try again, or maybe don't

Give one city to the thugs so they can all live together. I vote for Chicago where they have strict gun laws.

[billeisele 130]

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so 3.999999 .... = 4?

Steve - sometimes close is good enough

if I was in a bar looking for a 10, and found a 9.999999, that would be close enough

math is the language of numbers, in axiomatic geometry lines can cross and not touch - once you get your head around that anything is possible

Give one city to the thugs so they can all live together. I vote for Chicago where they have strict gun laws.

[shropshire 0]

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That's nothing...check this out:

Let...

a=1
b=1

That means

a=b

multiply both sides by a
a2 = ab

----------------
not where I come from
a2 = 2
ab = 1

try again, or maybe don't

um .... 1*1 = 1 on my planet

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[likearock 2]

Quote

Quote

That's nothing...check this out:

Let...

a=1
b=1

That means

a=b

multiply both sides by a
a2 = ab

----------------
not where I come from
a2 = 2
ab = 1

try again, or maybe don't

um .... 1*1 = 1 on my planet

The OP wrote a2 to mean a squared. If you read it that way, the "proof" does follow logically. Except, of course, for the divide by zero you already pointed out, which nullifies the whole deal.

[shropshire 0]

I believe that he did mean Squared (typically, I see a2 and a^2 but 2a would imply 2 x a). - but it was a [very] long time since I was at school.

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[kallend 2,027]

Once you're dealing with infinities things get wierd in a hurry.

Infinity +1 = infinity

Infinity *2 = infinity

Infinity * infinity = infinity

BUT

2^infinity = (a bigger infinity)

There are an infinite number of integers, but there are more real numbers, so the number of real numbers is uncountable, since there aren't enough integers to count them with.

...

The only sure way to survive a canopy collision is not to have one.

[pirana 0]

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That's nothing...check this out:

Let...

a=1
b=1

That means

a=b

multiply both sides by a
a2 = ab

Subtact b2 from both sides
a2 - b2 = ab - b2
Factor

(a+b)(a-b) = b(a-b)

Divide both sides by (a-b)
*crosses out both (a-b)*

a+b=b

If
a=1 and b=1

Then
1+1=1
2=1

Factoring error.

(a+b)(a-b) is not a square minus b square.

" . . . the lust for power can be just as completely satisfied by suggesting people into loving their servitude as by flogging them and kicking them into obedience." -- Aldous Huxley