Here you can keep your brain fit by solving math related problems and also earn SBI or sometimes other rewards by doing so.
The problems usually contain a mathematical equation that in my opinion is fun to solve or has an interesting solution.
I will also only choose problems that can be solved without additional tools(at least not if you can calculate basic stuff in your head), so don't grab your calculator, you won't need it.
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Rules

No upvote, No resteem, No follow required!

I will give 1 SBI to 1 random person who put a correct or partly correct solution of the problem in a comment.

I will give 10 STEM to every participant. I hope that you stake them, but They will be yours, so you can do with them whatever you want.

You have 4 days to solve it.

And one more thing: If there are infinitely many solutions, I only want general solutions or integer solutions!

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Problem

Today I want to give you something interesting about infinite sums.
What is the result of the following sum:
1-1+1-1+1-1+1-1+…
(… means that there are infinitely many terms following the same pattern)
Here the same expression with more fancy math symbols:

What do you think is the solution and why?

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To everyone who already participated in a past contest, come back today and try a new problem(tell me if you don't want to be tagged):
@addax @ajayyy @athunderstruck @bwar @contrabourdon @golddeck @heraclio @hokkaido @iampolite @masoom @mmunited @mobi72 @mytechtrail @ninahaskin @onecent @sidekickmatt @sparkesy43 @syalla @tonimontana @vote-transfer @zuerich

In case no one gets a result(which I doubt), I will give away the prize to anyone who comments.

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@contrabourdon sponsors this contest with 2 STEEM weekly.
You can support him by using a witness vote on untersatz, so he can further support this and other contests.

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Announcement

I decided to make a change in my contest schedule.
This is partly because it is hard to think of new math problems twice a week and also because I want to expand to other regions of STEM.
I will make only one "Math Contest" every week.
In exchange I will also start a new, slightly different contest, which I will post one day after the Math Contest.
→ I will still make 2 contests a week, but the contests and their results will be mostly scattered around the weekend and you get more time for both of them(4 days).