Alexander L
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 Sep30 awarded Explainer Sep24 awarded Autobiographer May6 answered Derivative of $e^{-x}$ Apr30 comment Rubik's cube puzzle Could we cut the Rubik's cube in such a way that the cross-section is in the shape of a hexagon? Apr30 answered I want a clear explanation for the Principle of Strong Mathematical Induction Apr27 revised Best self study math books? Grammar was cleaned up. Apr27 suggested approved edit on Best self study math books? Apr27 answered Best self study math books? Apr27 comment Combinatorial Mystery Function I was confused at first about the notation, so I sat down and tried again and got $\frac{(e_1+e_2+...+e_n -1)!}{e_1!e_2!...e_n!}$. Which I'm guessing is the same as your result. Thanks! Apr27 accepted Combinatorial Mystery Function Apr26 comment Showing that $f_{2n+1}=f_{n+1}^2+f_n^2$. There is actually an interesting article about this interpretation of the Fibonacci sequence in this month's Mathematics Magazine for those who are curious about some more of its utility in proofs. Apr26 awarded Editor Apr26 comment Combinatorial Mystery Function Thanks! I fixed the abusive notation. Apr26 revised Combinatorial Mystery Function Made notation less abusive. Apr25 answered Showing that $f_{2n+1}=f_{n+1}^2+f_n^2$. Apr25 awarded Scholar Apr25 accepted Non-linear Recursion Apr25 awarded Supporter Apr25 comment Show that $a，b, \sqrt{a}+ \sqrt{b} \in\mathbb Q \implies \sqrt{a},\sqrt{b} \in\mathbb Q$ Sorry, I didn't read the part about not being computational. Also, this just boils down to Bill Dubuque's proof. Apr25 answered Show that $a，b, \sqrt{a}+ \sqrt{b} \in\mathbb Q \implies \sqrt{a},\sqrt{b} \in\mathbb Q$