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 Dec7 awarded Popular Question Oct13 awarded Popular Question Sep2 awarded Notable Question Aug25 awarded Popular Question Jul2 awarded Curious May16 accepted Coefficients of exponential generating functions May15 asked Obtaining PDF of continuous random variable from CDF May15 comment TI Nspire CX CAS fails to perfrom basic integration yes, I do understand it. May15 comment TI Nspire CX CAS fails to perfrom basic integration exactly, the same thing happens in Wolfram Alpha (aka web-based Mathematica) May15 comment TI Nspire CX CAS fails to perfrom basic integration that's what I presume the problem is too. Is there any way to define $y \neq 0$ on the Nspire CX? May15 revised TI Nspire CX CAS fails to perfrom basic integration added 3 characters in body May15 asked TI Nspire CX CAS fails to perfrom basic integration May5 awarded Quorum Apr16 comment Proving corollary to Euler's formula by induction Ah, ok; perfect! Thanks for the clear explanation! Apr16 comment Proving corollary to Euler's formula by induction Ah, ok. So if the walk is not closed then I need to count each edge twice, right? But yes, once this information is clear I should be able to convince myself of that. Apr16 accepted Proving corollary to Euler's formula by induction Apr16 revised Proving corollary to Euler's formula by induction added 165 characters in body Apr16 revised Proving corollary to Euler's formula by induction Added LaTeX Apr16 asked Proving corollary to Euler's formula by induction Apr16 comment Prove that if graph $G$ is a 3-connected planar graph then its dual must be simple. Since a cycle must return to its starting vertex, a cycle beginning in $G_1$ must end in $G_1$ (it may or may not cross into $G_2$). In other words, the cycle must cross the bridges between $G_1$ and $G_2$ never or an even number of times. So that means such a cycle can only occupy two of the three available edges or none at all. Supposing the first case, if we removed the 2-occupied edges as you suggest, aren't we going to get a self-loop in the dual going across the remaining edge, which is not a simple graph?