Cho x,y,z>0. CMR: \(16xyz\left(x+y+z\right)\le3\sqrt[3]{\left(x+y\right)^4\left(y+z\right)^4\left(z+x\right)^4}\)
1.Giả sử a,b,c là 3 số dương sao cho ax+b(1-x)>cx(1-x) với mọi giá trị của x. CMR khi đó với mọi giá trị của x ta cũng có
ax+c(1-x)>bx(1-x) và bx+c(1-x)>ax(1-x)
2.Cho các số thực x,y,z >0. CMR
\(16xyz\left(x+y+z\right)\le3\sqrt[3]{\left(x+y\right)^4.\left(y+z\right)^4.\left(x+z\right)^4}.\)
3.Giải các bất phương trình sau
\(\hept{\begin{cases}\sqrt{xy}+\sqrt{1-x}\le\\2\sqrt{xy-x}+\sqrt{x}=1\end{cases}\sqrt{x}}\)
2/ \(3\sqrt[3]{\left(x+y\right)^4\left(y+z\right)^4\left(z+x\right)^4}=3\left(x+y\right)\left(y+z\right)\left(z+x\right)\sqrt[3]{\left(x+y\right)\left(y+z\right)\left(z+x\right)}\)
\(\ge6\left(x+y\right)\left(y+z\right)\left(z+x\right)\sqrt[3]{xyz}\)
\(\ge6.\frac{8}{9}\left(x+y+z\right)\left(xy+yz+zx\right)\sqrt[3]{xyz}\)
\(\ge\frac{16}{3}\left(x+y+z\right)3\sqrt[3]{x^2y^2z^2}\sqrt[3]{xyz}=16xyz\left(x+y+z\right)\)
3/ \(\hept{\begin{cases}\sqrt{xy}+\sqrt{1-x}\le\sqrt{x}\\2\sqrt{xy-x}+\sqrt{x}=1\end{cases}}\)
Dễ thấy
\(\hept{\begin{cases}0\le x\le1\\y\ge1\end{cases}}\)
Từ phương trình đầu ta có:
\(\sqrt{x}-\sqrt{xy}\ge\sqrt{1-x}\ge0\)
\(\Leftrightarrow y\le1\)
Vậy \(x=y=1\)
Thôi giúp 2 bài thôi còn bài còn lại tự làm cho lớn :D
cho 3 số x,y,z \(\ge\)0 và x+y+z+\(\sqrt{xyz}\)=4
cmr \(\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-x\right)\left(4-z\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}=8+\sqrt{xyz}\)
Cho 3 số x;y;z > 0 thỏa mãn:
\(x+y+z+\sqrt{xyz}=4\)
Tìm \(A=\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-x\right)\left(4-z\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}\)
1. Tim x,y,z biet: \(\frac{1}{2}\left(x+y+z\right)-3=\sqrt{x-2}+\sqrt{y-3}+\sqrt{z-4}\)
2. Chox,y,z > 0 thoa man \(x+y+z+\sqrt{xyz}=4\) . Tinh \(A=\sqrt{x\left(4-y\right)\left(4-z\right)+\sqrt{y\left(4-z\right)\left(4-x\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}}\)
Cho x,y,z >0 và x+y+z+\(\sqrt{xyz}\)=4
Tính \(B=\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-z\right)\left(4-x\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}\)
\(x+y+z+\sqrt{xyz}=4\)
\(\Leftrightarrow xyz=\left(4-x-y-z\right)^2\)
\(\Leftrightarrow xyz=16+x^2+y^2+z^2-8x-8y-8z+2xy+2xz+yz\)
\(\sqrt{x\left(4-y\right)\left(4-z\right)}=\sqrt{x\left(16-4y-4z+yz\right)}=\sqrt{16x-4xy-4xz+xyz}\)
\(=\sqrt{16x-4xy-4xz+16+x^2+y^2+z^2-8x-8y-8z+2xy+2yz+2xz}\)
\(=\sqrt{8x-2xy-2xz+2yz+x^2+y^2+z^2-8y-8z+16}\)
\(=\sqrt{\left(-x+y+z-4\right)^2}=\left|y+z-x-4\right|=\left|y+z-x-\left(x+y+z+\sqrt{xyz}\right)\right|\)
\(=\left|-2x-\sqrt{xyz}\right|=2x+\sqrt{xyz}\) (Vì x > 0)
Tương tự : \(\sqrt{y\left(4-z\right)\left(4-x\right)}=2y+\sqrt{xyz}\) , \(\sqrt{z\left(4-x\right)\left(4-y\right)}=2z+\sqrt{xyz}\)
Suy ra \(B=2x+2y+2z+2\sqrt{xyz}=2\left(x+y+z+\sqrt{xyz}\right)=2.4=8\)
cho x,y,z>0 thỏa mãn x+y+z+\(\sqrt{xyz}\)=4. Tính giá trị biểu thức:
\(A=\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-z\right)\left(4-x\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}\)
Ta có \(x+y+z+\sqrt{xyz}=4\Rightarrow4x+4y+4z+4\sqrt{xyz}=16\)
Ta lại có \(\sqrt{x\left(4-y\right)\left(4-z\right)}=\sqrt{x\left(16-4y-4z+yz\right)}=\sqrt{x\left(4x+4\sqrt{xyz}+yz\right)}=\sqrt{4x^2+4x\sqrt{xyz}+xyz}=\sqrt{\left(2x+\sqrt{xyz}\right)^2}=2x+\sqrt{xyz}\)
Tương tự \(\sqrt{y\left(4-z\right)\left(4-x\right)}=2y+\sqrt{xyz}\)
\(\sqrt{z\left(4-x\right)\left(4-y\right)}=2z+\sqrt{xyz}\)
Suy ra \(P=\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-z\right)\left(4-x\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}=2x+\sqrt{xyz}+2y+\sqrt{xyz}+2z+\sqrt{xyz}-\sqrt{xyz}=2x+2y+2z+2\sqrt{xyz}=2\left(x+y+z+\sqrt{xyz}\right)=2.4=8\)
Cho x , y , z > 0 ; x + y + z +\(\sqrt{xyz}\)=4
Tính \(M=\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-x\right)\left(4-z\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}\)
cho x,y,z >o. CMR:
\(\frac{\sqrt{y+z}}{x}+\frac{\sqrt{x+z}}{y}+\frac{\sqrt{x+y}}{z}\ge\frac{4\left(x+y+z\right)}{\sqrt{\left(y+z\right)\left(z+x\right)\left(x+y\right)}}\)
Cho \(x,y,z>0\)thoả \(x+y+z+\sqrt{xyz}=4\)
Tính \(T=\sqrt{x\left(4-y\right)\left(4-z\right)}+\sqrt{y\left(4-z\right)\left(4-x\right)}+\sqrt{z\left(4-x\right)\left(4-y\right)}-\sqrt{xyz}\)
Ta có
\(\sqrt{x\left(4-y\right)\left(4-z\right)}=\sqrt{x\left[4\left(4-y-z\right)+yz\right]}\)
\(=\sqrt{x\left(4\left(x+\sqrt{xyz}\right)+yz\right)}\)
\(=\sqrt{4x^2+4x\sqrt{xyz}+xyz}\)
\(=2x+\sqrt{xyz}\)
Khi đó \(T=2\left(x+y+z\right)+3\sqrt{xyz}-\sqrt{xyz}=2.4=8\)