\(\Leftrightarrow8\left(a^3+b^3\right)\ge2\left(a^3+b^3\right)+6ab\left(a+b\right)\)
\(\Leftrightarrow a^3+b^3-ab\left(a+b\right)\ge0\)
\(\Leftrightarrow\left(a+b\right)\left(a^2-ab+b^2\right)-ab\left(a+b\right)\ge0\)
\(\Leftrightarrow\left(a+b\right)\left(a-b\right)^2\ge0\) luôn đúng
Cho a,b,c>0. CM các bđt sau:
a)\(\left(a^3+b^3+c^3\right)\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)\ge\left(a+b+c\right)^2\)
b)\(3\left(a^3+b^3+c^3\right)\ge\left(a+b+c\right)\left(a^2+b^2+c^2\right)\)
c)\(9\left(a^3+b^3+c^3\right)\ge\left(a+b+c\right)^3\)
Cho a,b,c∈R.CM bđt \(a^2+b^2+c^2\ge ab+bc+ca\) (1). Áp dụng cm các bđt sau:
a)\(\left(a+b+c\right)^2\le3\left(a^2+b^2+c^2\right)\)
b)\(\frac{a^2+b^2+c^2}{3}\ge\left(\frac{a+b+c}{3}\right)^2\)
c)\(\left(a+b+c\right)^2\ge3\left(ab+bc+ca\right)\)
d)\(a^4+b^4+c^4\ge abc\left(a+b+c\right)\)
e)\(\frac{a+b+c}{3}\ge\sqrt{\frac{ab+bc+ca}{3}}vớia,b,c>0\)
f)\(a^4+b^4+c^4\ge abc\) nếu a+b+c=1
Cho a,b,c>0 chứng minh \(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\ge\frac{9}{a+b+c}\) (1). Áp dụng chứng minh các BĐT sau:
a) \(\left(a^2+b^2+c^2\right)\left(\frac{1}{a+b}+\frac{1}{b+c}+\frac{1}{c+a}\right)\ge\frac{3}{2}\left(a+b+c\right)\)
b) Cho x,y,z>0 tm x+y+z=1. Tìm GTLN của bt \(P=\frac{x}{x+1}+\frac{y}{y+1}+\frac{z}{z+1}\)
Cho a, b, c. CMR:
\(\sqrt[3]{\left(\frac{2a}{b+c}\right)^2}+\sqrt[3]{\left(\frac{2b}{c+a}\right)^2}+\sqrt[3]{\left(\frac{2c}{a+b}\right)^2}\ge3\)
Cho các số thực dương a, b, c. CMR: \(\frac{a^4}{b^2\left(c+a\right)}+\frac{b^4}{c^2\left(a+b\right)}+\frac{c^4}{a^2\left(b+c\right)}\) ≥ \(\frac{a+b+c}{2}\)
\(a\frac{3}{5}-\left(-\frac{1}{2}\right)+\frac{2}{5} b\frac{3}{7}.19\frac{1}{3}-\frac{3}{7}.33\frac{1}{3}c\left(\frac{3^4}{5}\right).\left(\frac{5^3}{3}\right)d\frac{11}{23}-\frac{5}{41}+\frac{13}{24}+0,5-\frac{36}{41}\)
chứng minh
a , \(sinasin\left(\frac{\pi}{3}-a\right)sin\left(\frac{\pi}{3}+a\right)=\frac{1}{4}sin3a\) Áp dụng tính \(sin\frac{\pi}{9}sin\frac{2\pi}{9}sin\frac{4\pi}{9}\)
b , \(cosacos\left(\frac{\pi}{3}-a\right)cos\left(\frac{\pi}{3}+a\right)=\frac{1}{4}cos3a\) Áp dụng tính \(cos\frac{\pi}{18}cos\frac{5\pi}{18}cos\frac{7\pi}{18}\)
Bài 1 : Tìm x biết
a) \(13\frac{1}{3}\div1\frac{1}{3}=26\div\left(2x-1\right)\)
b) \(0,2:1\frac{1}{5}=\frac{2}{3}\div\left(6x+7\right)\)
c) \(\frac{37-x}{x+13}=\frac{3}{7}\)
d) \(\frac{x-1}{x+5}=\frac{6}{7}\)
e) \(2\frac{2}{\frac{3}{0,002}=}\frac{1\frac{1}{9}}{x}\)
Bài 2 : Tìm x,y,z biết:
a) \(\frac{x}{7}=\frac{4}{13}\)và x + y = 40
b) 3x = 2y , 7y = 57 và x - y + z = 32
c) \(\frac{x-1}{2}=\frac{y-2}{3}=\frac{7-4}{4}\)và 2x + 3y - z = 50
Bài 3 .
a) 6,88 : x =12:27
b) \(8\frac{1}{3}\div11\frac{2}{3}=13:\left(2x\right)\)
Giải giúp mk
Mk đng cần gấp
\(\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}\ge\frac{3}{2}\) với a,b,c>0
