[Math] Proving a limit does not exist with epsilon delta

epsilon-deltalimits

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I don't have an equation for this. I'm looking more for intuition rather than anything else. At what point in the epsilon-delta definition of a limit does this fail to hold up?

I'm having trouble understanding the epsilon-delta definition of a limit and why it's defined the way it is.

Best Answer

Call the size of the jump $a$. Choose $\varepsilon=a/2$. Then no matter how small you choose $\delta$, there will be $x$ (on the other side of the jump from $x_0$) such that $|x-x_0|<\delta$ and $|f(x)-f(x_0)|>\varepsilon$.