help me convince a friend that 0.333...=1

on April 3rd, I posted this in GQ:

My friend who I am arguing with 9and the whole reason I posted, to try and convince him) is still not convinced that 0.33333…=1

After seeing the post, he said:

[quote]

Hi. Have looked atthe linkvery briefly. First comment on “erislover” - 1/3+1/3+1/3=1/1=1

This is totally foolish because it is based on everybody accepting that 1/3=0.333…which is the actual problem. His whole way of trying to clear this up is to me very unscientific and illustrates the problem with getting info from the web.
This: [But the truth of it, without calculus, is the method you show: .333… is just a representation of one-third.] THIS is the whole problem, I say that this is an insufficient representation of one-third for theoretical math.

[end quote]

BUNK!!! B-U-N-K, BUNK!

Help me correct this guy!

please!
TJ

I only posted this in GD as it was already a closed thread in GQ- but I need more ammo to shoot down my friend!

The problem seems to be that he doesn’t accept that 1/3 is 0.3 recurring. Ask him what he thinks 1/3 is in decimal then?

Your friend is correct. .3333… =! 1

.333… + .333… + .333… on the otherhand…

As Telemark hints, you probably meant to gather arguments that 0.9… is equal to 1, not 0.3… Either that, or you’re impishly writing your numbers in base 4 without telling us.

Many threads on this board have addressed the topic before — although, having only a “Guest” account, you might not have access to the search feature so as to find them all. Two decent Web pages though can be found here and here. Google on “0.999 = 1” and you’ll find a bunch more.

The real challenge isn’t to prove that 0.9… = 1. The challenge is to count how many ways there are of proving it.

In base 4, .3… = 1. In base 5, .4… = 1. In base 16, .F… = 1.

The reason is quite simple. 0.a[sub]1[/sub]a[sub]2[/sub]a[sub]3[/sub]…[sub]R[/sub] is defined to be the series whose nth term is given by a[sub]n[/sub]/R[sup]n[/sup]. With a[sub]i[/sub] = 1 for all i, this can be shown to converge (by means that you can find in an algebra 2 textbook) to 1.

Does your friend know algebra 2?

Your friend seems to think that a decimal representation is a matter of opinion or an alternate theory or some such. He doesn’t seem to get it that .333… is – by its very definition – one third. If he can’t get that very basic definition, I see no reason to multiply anything by 3. He refuses the premise, and that’s where you have to convince him.

Here’s another simple algebra explanation, gleaned from this site:

x = .333…
10x = 3.333…
3.333… = 3 + .333… = 3 + x
10x = 3 + x
10x - x = 3 + x - x
9x = 3
x = 3/9 = 1/3

If your friend doesn’t understand simple algebra or still refuses to accept it, I suggest you stop attempting to teach pigs to sing.

This proof works equally well for .9999… equalling 1, by the way.