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Encyclopedia Galactica => Science => : z3ro February 09, 2013, 04:19:32 PM

: Maths with me guys...
: z3ro February 09, 2013, 04:19:32 PM
[Question]


What's the sum of     1 + 2 + 4 + 8 + 16 + ...  (continues to infinity with each number twice as large as the previous one)




Sum? ???   =  Infinity ∞ ?! Right?




....






But wait....  :o


1 * X = X    for any X  [OK?]


so the sum is similar to (1)(1+2+4+8+16+...)  [OK?]


Now, One is the same as (two minus one)


1 = (2-1)  [OK?]


So.. the sum is still the same as (2-1)(1+2+4+8+16+...)


If we multiply.....   ???  we get... ( 2+4+8+16+32+...... -1 + -2 + -4 + -8 + -16 + -32 +...)   We have


2 - 2 = 0
+4 + -4 =0
...etc...

Every number cancels out.. leaving... -1  8)






    (1+2+4+8+16+...) = -1
: Re: Maths with me guys...
: p_2001 February 09, 2013, 05:08:36 PM
no.... i'm not sure if this is a troll...

.. See, your cancellation has a flaw.
you are canceling the SECOND term of the negative series with first of the positive...

hence sum is
∞ - 1 = ∞ ...


you cannot forget the un-cancelled term.
: Re: Maths with me guys...
: Snayler February 09, 2013, 05:23:21 PM
So.. the sum is still the same as (2-1)(1+2+4+8+16+...)


If we multiply.....   ???  we get... ( 2+4+8+16+32+...... -1 + -2 + -4 + -8 + -16 + -32 +...)   We have


2 - 2 = 0
+4 + -4 =0
...etc...

Every number cancels out.. leaving... -1  8)

    (1+2+4+8+16+...) = -1


Your logic is flawed. If you multiply:
2[(2-1)(1+2+4+8+16+...)] =
2(2-1)*2(1+2+4+8+16+...) =
(4-2)*(2+4+8+16+32+...)
which is still infinity.
: Re: Maths with me guys...
: Kulverstukas February 09, 2013, 05:41:46 PM
You put too many spaces out of excitement.
: Re: Maths with me guys...
: DaNePaLI February 09, 2013, 05:46:21 PM
You put too many spaces out of excitement.
Lmfao. Exactly.
: Re: Maths with me guys...
: karsa February 09, 2013, 07:09:51 PM
You can't just write one equation, take a part of it and rewrite it to suite your needs. Well... sometimes you can but this is not the case. Rules must be followed and (2-1)*(1+2+4+8+...) is still equal to ∞ no matter what.
: Re: Maths with me guys...
: Jboeggs February 09, 2013, 07:39:33 PM
You are not multiplying, subtracting, or dividing. You are also not adding by a negative, which means the answer will always be a positive. The answer is always going to be infinite.