\(\frac{16}{3x+3y+2z}=\frac{16}{\left(x+y\right)+\left(x+y\right)+\left(x+z\right)+\left(y+z\right)}\le\frac{1}{x+y}+\frac{1}{x+y}+\frac{1}{x+z}+\frac{1}{y+z}\)
Tương tự:
\(\frac{16}{3x+2y+3z}\le\frac{1}{x+z}+\frac{1}{x+z}+\frac{1}{x+y}+\frac{1}{z+y}\)
\(\frac{16}{2x+3y+3z}\le\frac{1}{y+z}+\frac{1}{z+y}+\frac{1}{y+x}+\frac{1}{x+z}\)
\(\Rightarrow16P\le4\left(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{z+x}\right)=4\cdot6=24\)
\(\Rightarrow P\le\frac{3}{2}\) tại \(x=y=z=\frac{1}{4}\)
Cho \(x,y,z\) dương sao cho \(\dfrac{1}{x+y}+\dfrac{1}{y+z}+\dfrac{1}{z+x}=6\). Tìm giá trị lớn nhất của \(P=\dfrac{1}{3x+3y+2z}+\dfrac{1}{3y+3z+2x}+\dfrac{1}{3z+3x+2y}\)
Cho x,y,z>=0 và x+y+z=1. Tìm MaxP=(x+2y+3z)(6x+3y+2z)
Cho x ; y ; z > 0 thỏa mãn \(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{z+x}=6\)
Tìm \(P_{max}=\frac{1}{3x+3y+2z}+\frac{1}{3x+2y+3z}+\frac{1}{2x+3y+3z}\)
Cho x;y;z dương sao cho \(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{z+x}=6\).
Tính giá trị lớn nhất của P=\(\frac{1}{3x+3y+2z}+\frac{1}{3y+3z+2x}+\frac{1}{3z+3x+2y}\)
Cho x, y, z dương thỏa mãn: \(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{x+z}=6\)
Chứng minh: \(\frac{1}{3x+3y+2z}+\frac{1}{3x+2y+3z}+\frac{1}{2x+3y+3z}\le\frac{3}{2}\)
Cho x,y,z thuộc R+ thỏa mãn:
\(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{x+z}=6\)
CMR: \(\frac{1}{3x+3y+2z}+\frac{1}{3x+2y+3z}+\frac{1}{2x+3y+3z}\le\frac{3}{2}\)
Cho x,y,z>0 và \(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{z+x}=6\)
Chứng minh \(\frac{1}{3x+3y+2z}+\frac{1}{3x+2y+3z}+\frac{1}{2x+3y+3z}\le\frac{3}{2}\)
cho x,y,z thoả mãn :
\(\frac{1}{x+y}+\frac{1}{y+z}+\frac{1}{z+x}=12\)
chứng minh: \(\frac{1}{2x+3y+3z}+\frac{1}{3x+2y+3z}+\frac{1}{3x+3y+2z}\le3\)
\(\hept{\begin{cases}3x^2+2y+1=2z\left(x+2\right)\\3y^2+2z+1=2x\left(y+2\right)\\3z^2+2x+1=2y\left(z+2\right)\end{cases}\Leftrightarrow\hept{\begin{cases}3x^2+2y+1=2xz+4z\\3y^2+2z+1=2xy+4x\\3z^2+2x+1=2yz+4y\end{cases}}}\)
Cộng 3 vế vào rồi chuyển vế ta được
\(2x^2+2y^2+2z^2-2xy-2yz-2zx+\left(x^2+2x+1\right)+\left(y^2+2y+1\right)+\left(z^2+2z+1\right)=0\)
\(\Leftrightarrow\left(x-y\right)^2+\left(y-z\right)^2 +\left(z-x\right)^2+\left(x+1\right)^2+\left(y+1\right)^2+\left(z+1\right)^2=0\)
Dễ thấy VP > 0
Dấu "=" khi x = y = z = -1
