ՃՃՃ
Reputation
Next privilege 50 Rep.
Comment everywhere
 Sep 2 awarded Altruist Sep 1 awarded Investor Jul 23 comment Prove $\sqrt{k}$ is not a rational number. math.stackexchange.com/questions/4467/… Jul 18 awarded Citizen Patrol Jul 17 answered Find the limit if it exists. Multivariable calculus Jul 16 comment How to solve this simple integral with substitution and partial fraction decomposition No problem.${}$ Jul 16 comment How to solve this simple integral with substitution and partial fraction decomposition After the substitution you should get $\displaystyle\int\frac{u^2}{(u-1)^3}\dfrac{du}{2u}=\frac12 \int\frac{u}{(u-1)^3}du$. Jul 16 answered How to solve this simple integral with substitution and partial fraction decomposition Jul 16 comment Proving there exist an infinite number of real numbers satisfying an equality Are you sure that is the correct stactement? Jul 16 comment Find equation of the plane through the origin with basis <1,2,-1> and <2,3,4>. Yes, the vector you get when you compute the cross product is a normal vector to the plane. Since you got $11i-6j-k$ as normal vector, an equation for the plane is $11x-6y-z=0$. And don't worry, we are all learning. :) Jul 16 comment Find equation of the plane through the origin with basis <1,2,-1> and <2,3,4>. Yes, that's the cross product. No, that's not an equation. Given a normal vector $ai+bj+ck$ to a plane $P$ through the origin, an equation for $P$ is given by $ax+by+cz=0$. Jul 16 answered Find equation of the plane through the origin with basis <1,2,-1> and <2,3,4>. Jul 15 comment Find the characteristic polynomial of a matrix You're welcome. :) Jul 15 answered Find the characteristic polynomial of a matrix May 28 comment finite additivity condition I'm afraid I don't get what you mean. You're given a finite number of disjoint sets, say, $A_1,\cdots ,A_N$, and you want to prove $P(\bigcup_{n=1}^NA_n)=\sum_{n=1}^N P(A_n)$. So you construct a sequence $(B_n)_{n\in\Bbb N}$ setting $B_k=A_k$ for $1\le k\le N$ and $B_k=\emptyset$ for $k>N$. Then you apply the countable aditivity property to $B_1,B_2,\cdots$. What do you get? May 28 comment finite additivity condition Just set $A_n=\emptyset$ for $n>N$. May 26 comment Proving that either $2^n-1$ or $2^n+1$ is not prime One of them must be divisible by 3. May 25 comment Is $1847^{2013}+2$ really a prime? Mathematica says it is prime... it took less than a minute. May 25 comment Sequences with the following properties… What if $b_n$ is not positive? May 25 comment If $2^x=0$, find $x$. @user42912 there's no problem at all. You're free to upvote anything you want, and that's why I deleted my comment. :)