\(\forall a,b,c\ge0\).Áp dụng BĐT Caushy-Schwarz,ta có :
\(VT\ge\frac{\left(1+1+1\right)^2}{2a+c+2c+a+2a+b}=\frac{9}{3\left(a+b+c\right)}=\frac{3}{a+b+c}\)
Dấu "=" xảy ra khi a=b=c
Chương 4: BẤT ĐẲNG THỨC, BẤT PHƯƠNG TRÌNH
Các câu hỏi tương tự
cho các số thực a,b,c dương chứng minh rằng a+b+c≤\(\frac{1}{2}\left(a^2b+b^2c+c^2a+\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)\)
cho a,b,c,d >0 thỏa a+b+c+d=4 chứng minh \(\frac{a}{1+b^2c}+\frac{b}{1+c^2a}+\frac{c}{1+d^2a}+\frac{d}{1+a^2b}\)
1) \(\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}\ge\frac{3}{2}\)
2) với \(\left\{{}\begin{matrix}a,b,c>0\\a+b+c=3\end{matrix}\right.\) chứng minh \(\frac{a^3}{b\left(2c+a\right)}+\frac{b^3}{c\left(2a+b\right)}+\frac{c^3}{a\left(2b+c\right)}\ge1\)
Cho a, b, c dương.
Cmr: \(\frac{1}{2a+b+c}+\frac{1}{a+2b+c}+\frac{1}{a+b+2c}\le\frac{1}{a+3b}+\frac{1}{b+3c}+\frac{1}{c+3a}\)
cho a,b,c là các số thực dương thỏa mãn ab+bc+ca=3. CMR:
\(\frac{a}{2a^2+bc}+\frac{b}{2b^2+ca}+\frac{c}{2c^2+ab}\ge abc\)
cho \(c\ge b\ge a>0\) . Cmr: \(\frac{2a^2}{b+c}+\frac{2b^2}{c+a}+\frac{2c^2}{a+b}\le\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{a}\)
2. Cho a, b > 0. CM: \(\frac{1}{a}+\frac{1}{b}\ge\frac{4}{a+b}\)
Áp dụng CM các bđt sau:
a)Cho a, b, c > 0 thỏa mãn \(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=4.\) CM:\(\frac{1}{2a+b+c}+\frac{1}{a+2b+c}+\frac{1}{a+b+2c}\le1\)
b)\(\frac{ab}{a+b}+\frac{bc}{b+c}+\frac{ca}{c+a}\le\frac{a+b=c}{2}\left(a,b,c>0\right)\)
cho a,b,c > 0 thỏa mãn \(\frac{1}{2a+1}+\frac{1}{2b+1}+\frac{1}{2c+1}\ge1\)
Cmr: \(\frac{1}{6a+1}+\frac{1}{6b+1}+\frac{1}{6c+1}\ge\frac{3}{7}\)
cho a,b,c> 0 . Cmr:
\(2\left(\frac{a}{b+2c}+\frac{b}{c+2a}+\frac{c}{a+2b}\right)\ge1+\frac{b}{b+2a}+\frac{c}{c+2b}+\frac{a}{a+2c}\)