Update maths/area.py

[taseikyo]

The parameters of the geometric shapes should be non-negative values

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

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• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
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[realDuYuanChao]

LGTM.

[cclauss]

in these algorithms, does it make sense for the radius to be 0?

[realDuYuanChao]

Yes. It does not make sense if radius equal 0. Should we revert this PR ?

[cclauss]

No need to revert. Just create a new PR to improve things.

[taseikyo]

I think it makes sense for the radius to be 0, which means the shape doesn't exist. So, when I wrote the code yesterday, I set the condition to be non-negative.