306 reputation
15
bio website
location Chengdu, China
age
visits member for 3 years, 1 month
seen 33 mins ago

Hi, everybody! Originally I am a mechanical engineer, however, I am very interested in computer science. One of my good friends is a professional developer, and I like to discuss and write some codes with him. Fortunately, I find this great website and I really hope I could make some friends here.


Sep
24
awarded  Autobiographer
Aug
1
comment How find the maximum of the value $x^2_{1}+x^2_{2}+\cdots+x^2_{2014}$
Sorry,. You have edited it. Originally it's -11k+ 5(2014-k) + x_2014 =0. I'm reading the post on my phone, and I can't see the updates immediately.
Aug
1
awarded  Commentator
Aug
1
comment How find the maximum of the value $x^2_{1}+x^2_{2}+\cdots+x^2_{2014}$
There are (2013-k) 5 (ideally, there should be (2014-k) 5, but this condition won't lead to an integer solution), so your equation should be corrected and so should the maximum.
Nov
5
awarded  Yearling
Feb
13
comment Is $\int_a^b f(x) dx = \int_{f(a)}^{f(b)} f^{-1}(x) dy$?
@Peter Because the op guessed $\int_a^b f(x) dx = (f(b)-f(a))b - \int_{f(a)}^{f(b)}f^{-1}(x)dx$ , I just wan to show him his guess is close to the fact.
Feb
7
awarded  Supporter
Feb
7
comment Is $\int_a^b f(x) dx = \int_{f(a)}^{f(b)} f^{-1}(x) dy$?
Furthermore, we can get $\int_a^b f(x)dx = x f(x)|_a^b - \int_a^b x f'(x)dx = x f(x)|_a^b - \int_a^b f^{-1}(f(x)) f'(x)dx=x f(x)|_a^b - \int_{f(a)}^{f(b)} f^{-1}(u) du(u=f(x))=x f(x)|_a^b - \int_{f(a)}^{f(b)} f^{-1}(x) dx $, so your guess is close to the fact that $\int_a^b f(x) dx = bf(b)-af(a) - \int_{f(a)}^{f(b)}f^{-1}(x)dx$
Dec
8
revised Why is arctan of $-\frac{\sqrt{3}}{3} = -\frac{1}{6}\pi$?
In my opinion,a open interval should be noted as" (a, b)", instead of " ]a,b[". A typo?
Dec
8
suggested approved edit on Why is arctan of $-\frac{\sqrt{3}}{3} = -\frac{1}{6}\pi$?
Dec
6
comment Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
absolutely I am not offended.actually, thanks for your comment! I have much to learn here and I love math.
Dec
5
awarded  Editor
Dec
5
revised Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
added 376 characters in body
Dec
5
comment Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
@DylanMoreland: Sorry, I just typed my comment on my phone. You know, it's slower to type than on a computer. And I finished my comment without care. That's why I showed such a strange comment...
Dec
5
comment Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
of course,two points can't tell me that. However, I think a function in the form $f(x)=x^n,n\in \mathbb N$ is elementary and it's monotonicity in $[0,\infty)$ is obvious. I am not familiar with Math jargons in English, but I can show it.
Dec
5
comment Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
of course,two points can't tell me that. However, I think a function in the form $f(x)=x^n,n\in \mathbb N$ is an
Dec
5
answered Prove that the equation $x^{10000} + x^{100} - 1 = 0$ has a solution with $0 < x < 1$
Dec
3
answered how to find center of an arc given start point, end point, radius, and arc direction?
Dec
1
answered Any idea how to solve this equation?
Nov
28
answered Finding all functions $f$ satisfying $f'(t)=f(t)+\int_a^bf(t)dt$