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 Jan27 revised Find limit when $\theta$ tends to $0$ of $\tan(\theta) /\theta$ added 10 characters in body Jan7 answered Indefinite integral question. Jan6 reviewed Approve How to form a differential equation, given temperature and direction of heat flow Jan5 reviewed Reject Prove that $4$ is the only solution to $2+2$. Jan4 revised Graphs of functions with fractional powers: $x^{p/q}$ edited tags Jan1 comment Is this a solution to the indefinite integral of $e^{-x^2}$? This is a nice idea, but I'm sorry to tell you that there's proof that there is no elementary formula for the integral. If you're okay with a series, just expand $e^{-x^2}$ and integrate term by term. Dec30 accepted Doubts with differential geometry notation in Frankel Dec28 asked Doubts with differential geometry notation in Frankel Dec13 comment Can integration get the real value of $\pi$? @user3015600: You could, in principle, get $\pi$ with infinite precision. If you want any digit of the decimal expansion of $\pi$, there's a zillion formulas that you can use to get it. The problem is that we can never know all of them, not because math doesn't work, but simply because there's infinitely many of them and we don't have infinite time. Dec13 answered Can integration get the real value of $\pi$? Dec10 comment Explain complex numbers Also, I think this is a duplicate: math.stackexchange.com/questions/251665/… Dec10 comment Explain complex numbers @tandberg: You can't always explain something at a level the other person can understand. If your cousin is familiar with the plane and a bit of analytic geometry, you can make the connection there. Otherwise, I'm not sure. Dec6 awarded Custodian Dec6 reviewed Leave Open Are all good mathematicians fluent in computational aspects of mathematics Dec6 reviewed Edit Using Laplace transform to solve an IVP Dec6 revised Using Laplace transform to solve an IVP improved formatting Nov29 answered The arithmetic mean of $X$ when arithmetic mean of $X^2 = 29$. Nov25 comment $2\times2$ matrices are not big enough @MarcvanLeeuwen: The reason I made my comment is that yours seemed to imply that this isn't a very good example because it's not evident how to define a rotation matrix for $n > 2$ dimensions. I just wanted to make clear that $3$-dimensional rotation matrices are easy to define and don't commute, that's all. Nov24 comment $2\times2$ matrices are not big enough @MarcvanLeeuwen: Rotation matrices don't commute in three dimensions. Nov24 reviewed Edit How to prove the equation $\cos x=2x$ has only one solution?