Let $a,b,c\ge 0$

by khanhsy, Mar 29, 2025, 11:16 AM

Let $a,b,c\ge 0$ and $ab+bc+ca>0$. Prove
$$\sum_{cyc}\dfrac{1}{a^3+bc(b+c)} \ge \dfrac{1}{a^3+b^3+c^3}+\dfrac{4}{ab(a+b)+bc(b+c)+ca(c+a)}.$$

In triangle ABC prove that:

by khanhsy, Mar 29, 2025, 11:12 AM

My problem

by hacbachvothuong, Mar 29, 2025, 10:10 AM

Let $a, b, c$ be positive real numbers such that $ab+bc+ca=3$. Prove that:
$\frac{a^2}{a^2+b+c}+\frac{b^2}{b^2+c+a}+\frac{c^2}{c^2+a+b}\ge1$

Let $a,b,c$ be nonnegative real numbers. Prove that

by khanhsy, Mar 29, 2025, 9:21 AM

Let $a,b,c,$ be nonnegative real numbers such that $a+b+c=3$. Prove that:
$$\dfrac{1}{\sqrt{a^3+3bc}}+\dfrac{1}{\sqrt{b^3+3ca}}+\dfrac{1}{\sqrt{c^3+3ab}}\ge \dfrac{1}{\sqrt{a^3+b^3+c^3+abc}}+\dfrac{2\sqrt{2}}{\sqrt{(a+b)(b+c)(c+a)}}.$$
This post has been edited 3 times. Last edited by khanhsy, 4 hours ago
Reason: edit

Gheorghe Țițeica 2025 Grade 9 P2

by AndreiVila, Mar 28, 2025, 9:09 PM

Let $a,b,c$ be three positive real numbers with $ab+bc+ca=4$. Find the minimum value of the expression $$E(a,b,c)=\frac{a^2+b^2}{ab}+\frac{b^2+c^2}{bc}+\frac{c^2+a^2}{ca}-(a-b)^2.$$

Gheorghe Țițeica 2025 Grade 8 P2

by AndreiVila, Mar 28, 2025, 8:51 PM

Let $k\geq 2$ be a positive integer and $x_1,x_2,\dots ,x_k\in (0,1)$. Also, let $m_1,m_2,\dots ,m_k$ and $n_1,n_2,\dots ,n_k$ be integers. Define $$A=x_1^{m_1}x_2^{m_2}\dots x_k^{m_k},\quad B=x_1^{n_1}x_2^{n_2}\dots x_k^{n_k}.$$Let $$C=x_1^{\min(m_1,n_1)}x_2^{\min(m_2,n_2)}\dots x_k^{\min(m_k,n_k)}$$$$D=x_1^{\max(m_1,n_1)}x_2^{\max(m_2,n_2)}\dots x_k^{\max(m_k,n_k)}.$$Prove that $A+B\leq C+D$. When does equality hold?

Dorel Miheț

An inequality on triangles sides

by nAalniaOMliO, Mar 28, 2025, 8:26 PM

Numbers $a,b,c$ are lengths of sides of some triangle. Prove the inequality$$\frac{a}{b+c-a}+\frac{b}{c+a-b}+\frac{c}{a+b-c} \geq \frac{a+b}{2c}+\frac{b+c}{2a}+\frac{c+a}{2b}$$

Inspired by old results

by sqing, Mar 28, 2025, 3:10 PM

A problem with non-negative a,b,c

by KhuongTrang, Mar 4, 2025, 3:50 PM

Problem. Let $a,b,c$ be non-negative real variables with $ab+bc+ca\neq 0.$ Prove that$$\color{blue}{\sqrt{\frac{8a^{2}+\left(b-c\right)^{2}}{\left(b+c\right)^{2}}}+\sqrt{\frac{8b^{2}+\left(c-a\right)^{2}}{\left(c+a\right)^{2}}}+\sqrt{\frac{8c^{2}+\left(a-b\right)^{2}}{\left(a+b\right)^{2}}}\ge \sqrt{\frac{18(a^{2}+b^{2}+c^{2})}{ab+bc+ca}}.}$$Equality holds iff $(a,b,c)\sim(t,t,t)$ or $(a,b,c)\sim(t,t,0)$ where $t>0.$

Simple inequality

by sqing, Jul 24, 2017, 3:30 AM

In $\triangle ABC$ with length-side $a,b,c$ , prove that$$\frac{a}{b+c-a}+\frac{b}{c+a-b}+\frac{c}{a+b-c}\ge\frac{b+c-a}{a}+\frac{c+a-b}{b}+\frac{a+b-c}{c}\ge3 .$$

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