# yiyi

 Apr 5 awarded Popular Question Feb 26 awarded Famous Question Feb 26 awarded Notable Question Feb 22 awarded Revival Jan 25 awarded Yearling Jan 25 awarded Yearling Jan 20 awarded Popular Question Nov 27 awarded Notable Question Nov 14 awarded Notable Question Oct 28 answered True or False: If $f$ is differentiable at $a$ and $g$ is differentiable at $f(a)$, then $(g\circ f)''(a)=g'(f(a))f''(a)+g''(f(a))(f'(a))^2$ Oct 26 comment Rolling dice problemI also do not understand how you came to this answer. Oct 26 comment Rolling dice problem@AndréNicolas, Do you mean that distinguishable as in Dice1, dice2 and dice3? Organized counting would be the order we add them? Oct 26 comment Show that $\int_{x=a}^{x=b} f'(x) g(x) dx=f(b)g(b)-f(a)g(a)-\int_{x=a}^{x=b} g'(x)f(x)\, dx$why do you have $x=a$ and $x=b$ for the limits of the integral? I just haven't seen that notation before and wondering why and in which branch or location in the world it is used. Oct 26 accepted Prime number in a grid for an identity matrix?? Oct 26 accepted Find $m$ such that the roots of this polynomial are greater than -1. Oct 26 accepted Whats the mathematics behind this type of taking the rope out puzzle. Oct 26 accepted How do induction on a recursive defined function? Oct 26 comment Why are there active users who do not ask questions?@GerryMyerson I know that now from reading about him, and I was just trying to make a witty response and it wasn't very good. I just knew the guy loved to solve problems, and this site is not for problems that would expand mathematics - that would be math overflow. I could see him being like the users in the question posted, having a high score from answering so many questions here and then posting bounties on overflow. Oct 25 comment Why are there active users who do not ask questions?@GerryMyerson from wikipedia: Paul Erdős (1913–1996) was an influential mathematician who spent a large portion of his later life writing papers with a large number of colleagues, working on solutions to outstanding mathematical problems. --- What I heard of him is that he traveled to solve problems. Oct 24 revised Please help me understand the concept of variable, and differentiation of variables.added info because the OP changed it a bit.