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inequality
xytunghoanh   0
13 minutes ago
For $a,b,c\ge 0$. Let $a+b+c=3$.
Prove or disprove
\[\sum ab +\sum ab^2 \le 6\]
0 replies
xytunghoanh
13 minutes ago
0 replies
Inequalities
nhathhuyyp5c   2
N Yesterday at 4:11 PM by alexheinis
Let $x,y$ be positive reals such that $3x-2xy\leq 1$. Find $\min$ \[
M = \frac{1 - x^2}{x^2} + 2y^2 + 3x + \frac{24}{y} + 2025.
\]

2 replies
nhathhuyyp5c
Yesterday at 3:31 PM
alexheinis
Yesterday at 4:11 PM
Inequalities
sqing   2
N Yesterday at 3:29 PM by sqing
Let $ a,b>0   $ . Prove that
$$ \frac{a}{a^2+a +2b+1}+ \frac{b}{b^2+2a +b+1}  \leq  \frac{2}{5} $$$$ \frac{a}{a^2+2a +b+1}+ \frac{b}{b^2+a +2b+1}  \leq  \frac{2}{5} $$
2 replies
sqing
Yesterday at 4:01 AM
sqing
Yesterday at 3:29 PM
dirichlet
spiralman   1
N Yesterday at 3:02 PM by clarkculus
Let n be a positive integer. Consider 2n+1 distinct positive integers whose total sum is less than (n+1)(3n+1). Prove that among these 2n+1 numbers, there exist two numbers whose sum is 2n+1.
1 reply
spiralman
Monday at 9:36 AM
clarkculus
Yesterday at 3:02 PM
Graphs and Trig
Math1331Math   1
N Yesterday at 12:18 PM by Mathzeus1024
The graph of the function $f(x)=\sin^{-1}(2\sin{x})$ consists of the union of disjoint pieces. Compute the distance between the endpoints of any one piece
1 reply
Math1331Math
Jun 19, 2016
Mathzeus1024
Yesterday at 12:18 PM
Inequalities
sqing   1
N Yesterday at 11:55 AM by sqing
Let $a,b,c >2 $ and $ ab+bc+ca \leq 75.$ Show that
$$\frac{1}{a-2}+\frac{1}{b-2}+\frac{1}{c-2}\geq 1$$Let $a,b,c >2 $ and $ \frac{1}{a}+\frac{1}{b}+\frac{1}{c}\geq \frac{6}{7}.$ Show that
$$\frac{1}{a-2}+\frac{1}{b-2}+\frac{1}{c-2}\geq 2$$
1 reply
sqing
Yesterday at 11:31 AM
sqing
Yesterday at 11:55 AM
CSMC Question
vicrong   1
N Yesterday at 11:47 AM by Mathzeus1024
Prove that there is exactly one function h with the following properties

- the domain of h is the set of positive integers
- h(n) is a positive integer for every positive integer n, and
- h(h(n)+m) = 1+n+h(m) for all positive integers n and m
1 reply
vicrong
Nov 26, 2017
Mathzeus1024
Yesterday at 11:47 AM
Inequalities
sqing   5
N Yesterday at 11:23 AM by sqing
Let $a,b,c >1 $ and $ \frac{1}{a-1}+\frac{1}{b-1}+\frac{1}{c-1}=1.$ Show that$$ab+bc+ca \geq 48$$$$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\leq \frac{3}{4}$$Let $a,b,c >1 $ and $ \frac{1}{a-1}+\frac{1}{b-1}+\frac{1}{c-1}=2.$ Show that$$ab+bc+ca \geq \frac{75}{4}$$$$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\leq \frac{6}{5}$$Let $a,b,c >1 $ and $ \frac{1}{a-1}+\frac{1}{b-1}+\frac{1}{c-1}=3.$ Show that$$ab+bc+ca \geq 12$$$$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\leq \frac{3}{2}$$
5 replies
sqing
Yesterday at 9:04 AM
sqing
Yesterday at 11:23 AM
function
khyeon   1
N Yesterday at 11:16 AM by Mathzeus1024
Find the range of $m$ so that any two different points in the graph of the quadratic function $y=2x^2+\frac{1}{4}$ are not symmetrical to the straight line $y=m(x+2)$
1 reply
khyeon
Sep 10, 2017
Mathzeus1024
Yesterday at 11:16 AM
Find function
trito11   1
N Yesterday at 10:00 AM by Mathzeus1024
Find $f:\mathbb{R^+} \to \mathbb{R^+} $ such that
i) f(x)>f(y) $\forall$ x>y>0
ii) f(2x)$\ge$2f(x)$\forall$x>0
iii)$f(f(x)f(y)+x)=f(xf(y))+f(x)$$\forall$x,y>0
1 reply
trito11
Nov 11, 2019
Mathzeus1024
Yesterday at 10:00 AM
The centroid of ABC lies on ME [2023 Abel, Problem 1b]
Amir Hossein   2
N Yesterday at 8:56 AM by MITDragon
In the triangle $ABC$, points $D$ and $E$ lie on the side $BC$, with $CE = BD$. Also, $M$ is the midpoint of $AD$. Show that the centroid of $ABC$ lies on $ME$.
2 replies
Amir Hossein
Mar 12, 2024
MITDragon
Yesterday at 8:56 AM
\frac{1}{5-2a}
Havu   2
N Apr 24, 2025 by arqady
Let $a\ge b\ge c \ge \frac{1}{2}$ and $a^2+b^2+c^2=3$. Find minimum:
\[P=\frac{1}{5-2a}+\frac{1}{5-2b}+\frac{1}{5-2c}.\]
2 replies
Havu
Apr 23, 2025
arqady
Apr 24, 2025
\frac{1}{5-2a}
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Havu
44 posts
#1 • 1 Y
Y by cubres
Let $a\ge b\ge c \ge \frac{1}{2}$ and $a^2+b^2+c^2=3$. Find minimum:
\[P=\frac{1}{5-2a}+\frac{1}{5-2b}+\frac{1}{5-2c}.\]
This post has been edited 1 time. Last edited by Havu, Apr 24, 2025, 11:19 PM
Reason: Error
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Havu
44 posts
#2 • 1 Y
Y by cubres
buzzzzzzzzzz
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arqady
30248 posts
#4 • 1 Y
Y by cubres
Havu wrote:
Let $a,b,c \ge \frac{1}{2}$ and $a^2+b^2+c^2=3$. Find minimum:
\[P=\frac{1}{5-2a}+\frac{1}{5-2b}+\frac{1}{5-2c}.\]
The following inequality is also true.
Let $\{a,b,c\}\subset\left[\frac{1}{3},+\infty\right)$ such that $a^2+b^2+c^2=3.$ Prove that:
$$\frac{1}{5-2a}+\frac{1}{5-2b}+\frac{1}{5-2c}\geq1.$$
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