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submitted 1 week ago by [email protected] to c/[email protected]
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[-] [email protected] 10 points 1 week ago* (last edited 1 week ago)

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] 6 points 1 week ago

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

this post was submitted on 06 Jun 2025
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