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 Jan 10 comment Understanding meaning of $f''$ for $x^2$ and $x^4$ Apologies, yes, I meant the 2nd derivative is constant. Jan 10 comment Understanding meaning of $f''$ for $x^2$ and $x^4$ I understand your 1st and 2nd paragraphs, and that helps, so thank you. I now understand that $x^2$ and $x^4$ look the same only superficially. I don't understand your 3rd paragraph however. Jan 10 comment Understanding meaning of $f''$ for $x^2$ and $x^4$ Aaaaaahhh, that would explain the concavity thing. The red line is a constant curvature, the blue one is not! Gotcha. Thank you Jan 10 comment Understanding meaning of $f''$ for $x^2$ and $x^4$ @Daniel I know! Jan 10 comment Understanding meaning of $f''$ for $x^2$ and $x^4$ @BenLongo I didn't mean the function is increasing but that the gradient is. Jan 10 comment Understanding meaning of $f''$ for $x^2$ and $x^4$ What is wrong with saying that $y''>0$ means the gradient is increasing? May 10 comment What does the last range on a histogram represent? @Casteels "not really a precise mathematical construct" Ah, OK, got it! Cheers. "adding that extra end-point does not change the width" confuses me though, or are you just saying a point has no width by definition? I get that. May 10 comment What does the last range on a histogram represent? @Casteels The author is asking me to decide what the other groups are. The one you have suggested makes sense as $m$ can be equal to 100. However, this does not follow the pattern. Is it fair to just change the last group so that it 'makes sense'? Is it normal that we just go ahead and change the last group? Mar 9 comment What was the first bit of mathematics that made you realize that math is beautiful? (For children's book) What was their answer? Feb 12 comment What is a diffeomorphism? Sorry Muphrid but I can't accept your answer since I don't have enough rep here, I +1'd it though. I don't know why the question was migrated, I was only looking for a hand-wavy definition. Jan 20 comment How does one create a rotation about a given axis in $R^{3}$ from rotations about the other axes? This seemed to do the trick. Thanks @Shard ! Jan 20 comment How does one create a rotation about a given axis in $R^{3}$ from rotations about the other axes? While it is a very nice result, I'm not sure it actually answers the question in that the matrix $\bf{R_{\hat{u}}}$ would appear difficult to decompose. Sep 12 comment “Rules of thumb” to decide which convergence test is most appropriate If the answer was helpful, please consider marking it as accepted, this will give more interest in the question (rep for you) and more interest in the answer (rep for me). Sep 12 comment “Rules of thumb” to decide which convergence test is most appropriate Although performing the integral test is a long-winded process, it always gives you a definite answer and so it is a powerful tool (although, are Maple or Mathematica xD).