Áp dụng BĐT AM-GM: \(\dfrac{1}{2}\sqrt{\left(a+3b\right)\left(b+3a\right)}\le\dfrac{1}{4}\left(4a+4b\right)=a+b\)
Ta chứng minh: \(3\left(a+b\right)^2+4ab\ge2\left(a+b\right)\)
hay \(3\left(a+b\right)^2+4ab\ge2\left(a+b\right)\left(\sqrt{a}+\sqrt{b}\right)^2\)
\(\Leftrightarrow\left(a+b-2\sqrt{ab}\right)^2\ge0\)( đúng)
Dấu = xảy ra khi \(a=b=\dfrac{1}{4}\)
1. Giải các hpt sau:
a, \(\left\{{}\begin{matrix}x-y=4\\3x+4y=19\end{matrix}\right.\) b, \(\left\{{}\begin{matrix}x-\sqrt{3y}=\sqrt{3}\\\sqrt{3x}+y=7\end{matrix}\right.\)
2. Giải các hpt sau:
a, \(\left\{{}\begin{matrix}2-\left(x-y\right)-3\left(x+y\right)=5\\3\left(x-y\right)+5\left(x+y\right)=-2\end{matrix}\right.\) b, \(\left\{{}\begin{matrix}\dfrac{2}{x-2}+\dfrac{2}{y-1}=2\\\dfrac{2}{x-2}-\dfrac{3}{y-1}=1\end{matrix}\right.\)
c, \(\left\{{}\begin{matrix}x+y=24\\\dfrac{x}{9}+\dfrac{y}{27}=2\dfrac{8}{9}\end{matrix}\right.\) d, \(\left\{{}\begin{matrix}\sqrt{x-1}-3\sqrt{y+2}=2\\2\sqrt{x-1}+5\sqrt{y+2=15}\end{matrix}\right.\)
3. Cho hpt \(\left\{{}\begin{matrix}\left(m+1\right)x-y=3\\mx+y=m\end{matrix}\right.\)
a, Giải hpt khi m=\(\sqrt{2}\)
b, tìm giá trị của m để hpt có nghiệm duy nhất thỏa mãn: x+y>0
1. a) \(\left\{{}\begin{matrix}x,y,z>0\\xyz=1\end{matrix}\right.\). Tìm max \(P=\frac{1}{\sqrt{x^5-x^2+3xy+6}}+\frac{1}{\sqrt{y^5-y^2+3yz+6}}+\frac{1}{\sqrt{z^5-z^2+zx+6}}\)
b) \(\left\{{}\begin{matrix}x,y,z>0\\xyz=8\end{matrix}\right.\). Min \(P=\frac{x^2}{\sqrt{\left(1+x^3\right)\left(1+y^3\right)}}+\frac{y^2}{\sqrt{\left(1+y^3\right)\left(1+z^3\right)}}+\frac{z^2}{\sqrt{\left(1+z^3\right)\left(1+x^3\right)}}\)
c) \(x,y,z>0.\) Min \(P=\sqrt{\frac{x^3}{x^3+\left(y+z\right)^3}}+\sqrt{\frac{y^3}{y^3+\left(z+x\right)^3}}+\sqrt{\frac{z^3}{z^3+\left(x+y\right)^3}}\)
d) \(a,b,c>0;a^2+b^2+c^2+abc=4.Cmr:2a+b+c\le\frac{9}{2}\)
e) \(\left\{{}\begin{matrix}a,b,c>0\\a+b+c=3\end{matrix}\right.\). Cmr: \(\frac{a}{b^3+ab}+\frac{b}{c^3+bc}+\frac{c}{a^3+ca}\ge\frac{3}{2}\)
f) \(\left\{{}\begin{matrix}a,b,c>0\\ab+bc+ca+abc=4\end{matrix}\right.\) Cmr: \(\sqrt{ab}+\sqrt{bc}+\sqrt{ca}\le3\)
g) \(\left\{{}\begin{matrix}a,b,c>0\\ab+bc+ca+abc=2\end{matrix}\right.\) Max : \(Q=\frac{a+1}{a^2+2a+2}+\frac{b+1}{b^2+2b+2}+\frac{c+1}{c^2+2c+2}\)
1. \(\left\{{}\begin{matrix}a,b,c>0\\a+b+c=1\end{matrix}\right.\). Cmr: \(\frac{ab}{\sqrt{\left(1-c\right)^2\left(1+c\right)}}+\frac{bc}{\sqrt{\left(1-a\right)^2\left(1+a\right)}}+\frac{ca}{\sqrt{\left(1-b\right)^3\left(1+b\right)}}\le\frac{3\sqrt{2}}{8}\)
2. \(\left\{{}\begin{matrix}a,b,c>0\\a+b+c\le1\end{matrix}\right.\). Cmr: \(\frac{1}{a^2+b^2+c^2}+\frac{1}{ab\left(a+b\right)}+\frac{1}{bc\left(b+c\right)}+\frac{1}{ac\left(a+c\right)}\ge\frac{87}{2}\)
3. \(\left\{{}\begin{matrix}a,b,c>0\\ab+bc+ca=2abc\end{matrix}\right.\). Cmr: \(\frac{1}{a\left(2a-1\right)^2}+\frac{1}{b\left(2b-1\right)^2}+\frac{1}{c\left(2c-1\right)^2}\ge\frac{1}{2}\)
4. \(\left\{{}\begin{matrix}x,y,z>0\\x+y+z=2015\end{matrix}\right.\). Tìm min \(A=\frac{x^4+y^4}{x^3+y^3}+\frac{y^4+z^4}{y^3+z^3}+\frac{z^4+x^4}{z^2+x^2}\)
Mn giúp mk với ạ! Thanks nhiều
Cho các số dương a,b,c thỏa mãn \(\left\{{}\begin{matrix}a+b+c=2\\a^2+b^2+c^2=2\end{matrix}\right.\)
Chứng minh rằng: \(a\sqrt{\dfrac{\left(1+b^2\right)\left(1+c^2\right)}{1+a^2}}+b\sqrt{\dfrac{\left(1+a^2\right)\left(1+c^2\right)}{1+b^2}}+c\sqrt{\dfrac{\left(1+a^2\right)\left(1+b^2\right)}{1+c^2}}=2\)
Đặt \(\left\{{}\begin{matrix}a=\sqrt{2}\\b=\sqrt[3]{2}\end{matrix}\right.\). Chứng minh: \(\dfrac{1}{a-b}-\dfrac{1}{b}=a+b+\dfrac{a}{b}+\dfrac{b}{a}+1\)
1. a) cho \(1\le a,b,c\le2\). Tìm max \(P=\left(x+y\right)\left(\frac{1}{x}+\frac{1}{y}\right)\)
b) \(\left\{{}\begin{matrix}a,b,c\ge0\\a+b+c=1\end{matrix}\right.\). Cmr: \(\sqrt{\frac{3a^2+1}{3b^2+1}}+\sqrt{\frac{3b^2+1}{3c^2+1}}+\sqrt{\frac{3c^2+1}{3a^2+1}}\le\frac{7}{2}\)
2.a) \(a,b\ge0;c\ge1;a+b+c=2\). cmr: \(\left(6-a^2-b^2-c^2\right)\left(2-abc\right)\le8\)
b) \(\left\{{}\begin{matrix}a+b\le2\\a^2+b^2+ab=3\end{matrix}\right.\). Tìm max,min \(P=a^2+b^2-ab\)
Cho 3 số thực dương a,b,c thoả mãn điều kiện:
\(\left\{{}\begin{matrix}a+b+c=2\\a^2+b^2+c^2=2\end{matrix}\right.\)
Chứng minh rằng:
\(a\sqrt{\frac{\left(1+b^2\right)\left(1+c^2\right)}{1+a^2}}+b\sqrt{\frac{\left(1+a^2\right)\left(1+c^2\right)}{1+b^2}}+c\sqrt{\frac{\left(1+a^2\right)\left(1+b^2\right)}{1+c^2}}\)
1. Giải hpt : a) \(\left\{{}\begin{matrix}\sqrt{x}+\sqrt{y}+\sqrt{z}=\sqrt{2017}\\\sqrt[3]{\left(x+3\right)\left(y+3\right)\left(z+3\right)}=3+\sqrt[3]{xyz}\end{matrix}\right.\)
b) \(\left\{{}\begin{matrix}\sqrt{x+1}+\sqrt[4]{x-1}+\sqrt{y^4+2}=y\\x^2+2x\left(y-1\right)+y^2-6y+1=0\end{matrix}\right.\)
giải hpt: a,\(\left\{{}\begin{matrix}x+y-\sqrt{xy}=3\\\sqrt{x+1}+\sqrt{y+1}=4\end{matrix}\right.\) b,\(\left\{{}\begin{matrix}x+y=5+\sqrt{\left(x-1\right)\left(y-1\right)}\\\sqrt{x-1}+\sqrt{y-1}=3\end{matrix}\right.\)
