this post was submitted on 06 Jun 2025
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Math Memes

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[–] [email protected] 5 points 3 days ago* (last edited 3 days ago) (1 children)

You cannot differentiate a sum when the variable being differentiated is used to define the number of terms in the sum — unless you rewrite the sum as a closed-form, continuous expression. Even in Sigma notation as you used.

The act of summing “x terms” as you expressed in your sum is not itself a differentiable process.

Once you turn it into a continuous function (in this case x^2), then you can differentiate it.

The Leibnitz rule doesn’t do anything here because you still have an unextractable “x” that’s defining your summation.

[–] [email protected] 3 points 3 days ago

That makes sense, thanks. I knew someone would know better than me how to interpret that.