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# One minus one plus one minus one plus...

There are three types of people in this world:

Evaluate:

$\color{blue}{S}=1-1+1-1+1-1+\ldots$

Type 1

$\color{blue}{S}=(1-1)+(1-1)+(1-1)+\ldots=0+0+0+\ldots=\boxed{0}$

Type 2

$\color{blue}{S}=1-(1-1)-(1-1)-(1-1)-\ldots=1-0-0-0-\ldots=\boxed{1}$

But the $$\displaystyle 3^{rd}$$ type of people did like this:

$1-\color{blue}{S}=1-(1-1+1-1+\ldots)=1-1+1-1+1-1+\ldots = S$

$\Leftrightarrow 1-\color{blue}S=\color{blue}S \Rightarrow 2\color{blue}S=1 \Rightarrow \color{blue}S=\boxed{\frac{1}{2}}$

1 year, 2 months ago

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Even more here:

Evaluate : $S=1-2+3-4+5-6+ \ldots$

Type 1 : $S=1+(-2+3)+(-4+5)+ \ldots = 1+1+1+1+\ldots=\infty$

Type 2 : $S=(1-2)+(3-4)+(5-6)+ \ldots = -1-1-1-1+\ldots=-\infty$

Type 3 : They go to WolframAlpha, search this:

 1 sum(n from 1 to infty,(-1)^n*n) 

Which shows up that "The ratio test is inconclusive." and "The root test is inconclusive.", from which they implies that the sum is incosistent.

Type 4 : They go to Wikipedia and finds out that the sum is actually equal to $$1/4$$. · 1 year, 1 month ago

Wow! Awesome!

I also saw this video:

$1+2+3+4+\ldots=\frac{1}{12}$ · 1 year, 1 month ago

i guess u forgot the negative sign along with 1/12 · 1 year, 1 month ago

Wow, that's cool :))) · 1 year, 1 month ago

You forgot $$4^\text{th}$$ type of people; they say that this series diverges. · 1 year, 1 month ago

Its answer oscillates b/w 0 and 1 · 1 year, 1 month ago

Yes that's why it diverges. · 1 year, 1 month ago

Comment deleted Aug 29, 2015

What is that supposed to mean? · 1 year, 1 month ago

last one is pretty good · 1 year, 2 months ago

Gud 1 · 1 year, 1 month ago

Grandi series. · 1 year, 1 month ago