\(A=x-2\sqrt{xy}+3y-2\sqrt{x}+1=\left(x+y+1-2\sqrt{xy}-2\sqrt{x}+2\sqrt{y}\right)+\left(2y-2\sqrt{y}\right)\)

\(=\left(-\sqrt{x}+\sqrt{y}+1\right)^2+2\left(\sqrt{y}-\frac{1}{2}\right)^2-\frac{1}{2}\ge-\frac{1}{2}\)

\(\Rightarrow MinA=-\frac{1}{2}\Leftrightarrow\hept{\begin{cases}\sqrt{y}-\sqrt{x}+1=0\\\sqrt{y}-\frac{1}{2}=0\end{cases}}\Leftrightarrow\hept{\begin{cases}x=\frac{9}{4}\\y=\frac{1}{4}\end{cases}}\)

\(P=\dfrac{y}{x}+\dfrac{x}{y}+\left(\dfrac{x}{3y}+3xy+\dfrac{1}{3}+\dfrac{1}{3}\right)+12\left(xy+\dfrac{1}{9}\right)-2\)

\(P\ge2\sqrt{\dfrac{xy}{xy}}+4\sqrt[4]{\dfrac{3x^2y}{27y}}+12.2\sqrt{\dfrac{xy}{9}}-2\)

\(P\ge4\sqrt{\dfrac{x}{3}}+8\sqrt{xy}=4\left(2\sqrt{xy}+\sqrt{\dfrac{x}{3}}\right)=4\)

\(P_{min}=4\) khi \(x=y=\dfrac{1}{3}\)

\(A=x-2\sqrt{x}\left(\sqrt{y}+1\right)+\left(\sqrt{y}+1\right)^2-\left(\sqrt{y+1}\right)^2+3y+1\)

\(A=\left(\sqrt{x}-\sqrt{y}-1\right)^2-\left(y+2\sqrt{y}+1\right)+3y+1\)

\(A=\left(\sqrt{x}-\sqrt{y}-1\right)^2+2y-2\sqrt{y}\)

\(A=\left(\sqrt{x}-\sqrt{y}-1\right)^2+2\left(y-2.\sqrt{y}.\frac{1}{2}+\frac{1}{4}\right)-\frac{1}{2}\)

\(A=\left(\sqrt{x}-\sqrt{y}-1\right)^2+2\left(\sqrt{y}-\frac{1}{2}\right)^2-\frac{1}{2}\ge-\frac{1}{2}\forall x,y\ge0\)

Dấu "="\(\Leftrightarrow\hept{\begin{cases}\sqrt{x}-\sqrt{y}-1=0\\\sqrt{y}=\frac{1}{2}\end{cases}\Leftrightarrow\hept{\begin{cases}x=\frac{9}{4}\\y=\frac{1}{4}\end{cases}}}\)

Vậy......

\(\left(x-2\sqrt{xy}+y\right)+2y-2\sqrt{x}+1\)

<=>\(\left(\sqrt{x}-\sqrt{y}\right)^2-2\left(\sqrt{x}-\sqrt{y}\right)+1+2y-2\sqrt{y}\)

<=>\(\left(\sqrt{x}-\sqrt{y}-1\right)^2+2\left(y-\sqrt{y}+\frac{1}{2}-\frac{1}{2}\right)\)

<=>\(\left(\sqrt{x}-\sqrt{y}-1\right)^2+2\left(\sqrt{y}-\frac{1}{2}\right)^2-1\)

=>\(A\ge-1\)

dấu bằng xảy ra <=>....

Tick cho mình nha

A = \(x-2\sqrt{xy}+y+2y-2\sqrt{x}+1\)

= \(\left(\sqrt{x}-\sqrt{y}\right)^2-2\sqrt{x}+1+2y\)

vì \(\left(\sqrt{x}-\sqrt{y}\right)^2\ge0\) nên A\(\ge-2\sqrt{x}+1+2y\)

Vậy gtnn của A là -2... (*bạn tự biết ha?!)

p/s: theo mik nghĩ thì bài này làm vậy

sai rùi đồ ngu

\(2P=2x-4\sqrt{xy}+6y-4\sqrt{x}+4019\)

\(=\left(\left(x-4\sqrt{xy}+y\right)-\frac{2}{2}.\left(\sqrt{x}-2\sqrt{y}\right)+\frac{1}{4}\right)+\left(x-\frac{2.3.\sqrt{x}}{2}+\frac{9}{4}\right)+2\left(y-\frac{2\sqrt{y}}{2}+\frac{1}{4}\right)+4016\)

\(=\left(\left(\sqrt{x}-2\sqrt{y}\right)^2-\frac{2}{2}.\left(\sqrt{x}-2\sqrt{y}\right)+\frac{1}{4}\right)+\left(x-\frac{2.3.\sqrt{x}}{2}+\frac{9}{4}\right)+2\left(y-\frac{2\sqrt{y}}{2}+\frac{1}{4}\right)+4016\)

\(=\left(\sqrt{x}-2\sqrt{y}-\frac{1}{2}\right)^2+\left(\sqrt{x}-\frac{3}{2}\right)^2+2\left(\sqrt{y}-\frac{1}{2}\right)^2+4016\ge2016\)

\(\Rightarrow P\ge2008\)khi \(\hept{\begin{cases}x=\frac{9}{4}\\y=\frac{1}{4}\end{cases}}\)

tung hỏa mù hả sao tăng Hệ số lên làm gì?

​​căn x=a, căn y=b

​​P=(a^2+b^2-2ab-2a+2b+1)+(2b^2-2b+1/2)+2009+1/2-(1+1/2)

​P=(a-b-1)^2+2(b-1/2)^2+2008>=2008

​đăng thức b=1/2=>y=1/4; và a-1/2-1=0=>a=3/2=>x=9/4

​

chịu thua vô điều kiện xin lỗi nha : v

muốn biết câu trả lời lo mà sệt trên google ấy đừng có mà dis:v

\(A=\left[\left(\frac{1}{\sqrt{x}}+\frac{1}{\sqrt{y}}\right).\frac{2}{\sqrt{x}+\sqrt{y}}+\frac{1}{x}+\frac{1}{y}\right]:\frac{\sqrt{x^3}+y.\sqrt{x}+x\sqrt{y}+\sqrt{y^3}}{\sqrt{x^3y}+\sqrt{xy^3}}\)

\(\Leftrightarrow A=\left[\frac{\sqrt{x}+\sqrt{y}}{\sqrt{xy}}.\frac{2}{\sqrt{x}+\sqrt{y}}+\frac{x+y}{xy}\right]:\frac{\left(\sqrt{x}+\sqrt{y}\right)^3}{\sqrt{xy}\left(x+y\right)}\)

\(\Leftrightarrow A=\frac{2\sqrt{xy}+x+y}{xy}:\frac{\left(\sqrt{x}+\sqrt{y}\right)^3}{\sqrt{xy}\left(x+y\right)}\)

\(\Leftrightarrow A=\frac{\sqrt{xy}\left(x+y\right)}{xy\left(\sqrt{x}+\sqrt{y}\right)}\)

\(\Leftrightarrow A=\frac{\left(x+y\right)}{\sqrt{xy}\left(\sqrt{x}+\sqrt{y}\right)}\)

sai sót chỗ nào chỉ cho mk nhé. ý kia chốc nx làm nốt

a.\(DK:x,y>0\)

Ta co:

\(A=\frac{x+y+2\sqrt{xy}}{xy}.\frac{\sqrt{xy}\left(x+y\right)}{\left(x+y\right)\left(\sqrt{x}+\sqrt{y}\right)}=\frac{\sqrt{x}+\sqrt{y}}{\sqrt{xy}}\)

b.

Ta lai co:

\(A=\frac{\sqrt{x}+\sqrt{y}}{\sqrt{xy}}\ge\frac{2\sqrt{\sqrt{x}.\sqrt{y}}}{4}=1\)

Dau '=' xay ra khi \(x=y=4\)

Vay \(A_{min}=1\)khi \(x=y=4\)