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a) A xác định khi \(\left\{{}\begin{matrix}x>0\\\sqrt{x}-3\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>0\\\sqrt{x}\ne3\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}x>0\\x\ne9\end{matrix}\right.\)
b)Với \(x>0;x\ne9\), ta có:
\(A=\frac{\sqrt{x}+1}{\sqrt{x}-3}=\frac{\sqrt{x}-3+4}{\sqrt{x}-3}=1+\frac{4}{\sqrt{x}-3}\)
Để A đạt giá trị nguyên thì \(\frac{4}{\sqrt{x}-3}\) đạt giá trị nguyên
Hay\(4⋮\left(\sqrt{x}-3\right)\)
Suy ra \(\sqrt{x}-3\inƯ\left(4\right)=\left\{\pm1;\pm2;\pm4\right\}\)
TH1: \(\sqrt{x}-3=\pm1\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-3=1\\\sqrt{x}-3=-1\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=4\\\sqrt{x}=2\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=16\\x=4\end{matrix}\right.\)
TH2: \(\sqrt{x}-3=\pm2\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-3=2\\\sqrt{x}-3=-2\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=5\\\sqrt{x}=1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=25\\x=1\end{matrix}\right.\)
TH3: \(\sqrt{x}-3=\pm4\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-3=4\\\sqrt{x}-3=-4\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=7\\\sqrt{x}=-1\left(Loại\right)\end{matrix}\right.\Rightarrow x=49\)
Vậy \(x\in\left\{1;4;16;25;49\right\}\)
A=\(\left(\frac{\sqrt{x}}{\sqrt{x}+1}-\frac{1}{x+\sqrt{x}}\right)\):\(\left(\frac{1}{\sqrt{x}+1}+\frac{2}{x-1}\right)\)Đk x>0 x#0 x#1
=\(\frac{x-1}{\sqrt{x}\left(\sqrt{x-1}\right)}\):\(\frac{\sqrt{x}-1+2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)
=\(\frac{\sqrt{x}+1}{\sqrt{x}}:\frac{\sqrt{x}+1}{\left(\sqrt{x-1}\right)\left(\sqrt{x}+1\right)}\)
=\(\frac{\sqrt{x}+1}{\sqrt{x}}:\frac{1}{\sqrt{x}-1}\)
=\(\frac{\sqrt{x}+1}{\sqrt{x}}.\sqrt{x}-1\)
=\(\frac{x-1}{\sqrt{x}}\)
Ta có 3+\(2\sqrt{2}=\left(\sqrt{2}+1\right)^2\)(thay và A ta dc
=>\(\frac{3+2\sqrt{2}-1}{\sqrt{2}+1}\)
= \(\frac{2\sqrt{2}+2}{\sqrt{2}+1}\)
=2
mk nhầm....\(\frac{x-1}{\sqrt{x}}>0\)=> \(x-1>0\Rightarrow x>1\)
mk làm r nhé
a) \(P=\frac{x^2-9}{x-3}+\frac{4-4\sqrt{x}+x}{2-\sqrt{x}}+\frac{4-x}{2+\sqrt{x}}\)
\(=\frac{\left(x-3\right)\left(x+3\right)}{x-3}+\frac{\left(2-\sqrt{x}\right)^2}{2-\sqrt{x}}+\frac{\left(2-\sqrt{x}\right)\left(2+\sqrt{x}\right)}{2+\sqrt{x}}\)
\(x+3+2-\sqrt{x}+2-\sqrt{x}\) = \(x+7-2\sqrt{x}\)
b) Tại x = 9, ta có:
P = \(x+7-2\sqrt{x}\) = 9 + 7 - 2\(\sqrt{9}\) = 10
đkxđ \(x\ne1;x\ge0\)
\(P=\frac{\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}-\frac{x-2}{\left(\sqrt{x}\right)^3-1}+\frac{\sqrt{x}+1}{x+\sqrt{x}+1}\)
\(P=\frac{1}{\sqrt{x}-1}-\frac{x-2}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}+\frac{\sqrt{x}+1}{x+\sqrt{x}+1}\)
\(P=\frac{x+\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}-\frac{x-2}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}+\frac{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)
\(P=\frac{x+\sqrt{x}+1-x+2+x-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)
\(P=\frac{x+\sqrt{x}+2}{\left(\sqrt{x}\right)^3-1}\)
a.\(ĐKXĐ:\left\{{}\begin{matrix}x\ge0\\x\sqrt{x}-1\ne0\\\sqrt{x}-1\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)\ne0\\\sqrt{x}-1\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ge0\\x\ne1\end{matrix}\right.\)
b.\(Q=\frac{x+2}{x\sqrt{x}-1}+\frac{\sqrt{x}+1}{x+\sqrt{x}+1}-\frac{1}{\sqrt{x}-1}\)
\(=\frac{x+2}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}+\frac{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}-\frac{x+\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)(do \(x\sqrt{x}-1=\sqrt{x}^3-1=\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)\))
\(=\frac{x+2+x-1-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)
\(=\frac{\sqrt{x}\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\)
\(=\frac{\sqrt{x}}{x+\sqrt{x}+1}\)
c.Để \(Q=\frac{2}{7}\) thì \(\frac{\sqrt{x}}{x+\sqrt{x}+1}=\frac{2}{7}\)
\(\Leftrightarrow7\sqrt{x}=2x+2\sqrt{x}+2\)
\(\Leftrightarrow2x-5\sqrt{x}+2=0\)
\(\Leftrightarrow2x-4\sqrt{x}-\sqrt{x}+2=0\)
\(\Leftrightarrow2\sqrt{x}\left(\sqrt{x}-2\right)-\left(\sqrt{x}-2\right)=0\)
\(\Leftrightarrow\left(\sqrt{x}-2\right)\left(2\sqrt{x}-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}-2=0\\2\sqrt{x}-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\sqrt{x}=2\\\sqrt{x}=\frac{1}{2}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=4\\x=\frac{1}{4}\end{matrix}\right.\)(Thỏa mãn đkxđ)
\(A=\frac{-7x^2}{\sqrt{x-3}-2}\)
\(đkxđ\Leftrightarrow\hept{\begin{cases}\sqrt{x-3}-2\ne0\\x-3>0\end{cases}}\)
\(\sqrt{x-3}-2\ne0\Rightarrow\sqrt{x-3}\ne2\)
\(\Rightarrow x-3\ne4\Leftrightarrow x\ne7\)
\(x-3>0\Leftrightarrow x>3\)
Vậy điều kiện xác định của A là \(\hept{\begin{cases}x>3\\x\ne7\end{cases}}\)
ĐKXĐ:
\(\sqrt{x-3}\ge0\Rightarrow\sqrt{x-3}-2\ge-2\)
\(\Rightarrow x\ge3\)
Mà \(\sqrt{x-3}-2\ne0\) \(\Rightarrow x\ne7\)
Vậy \(x\ge3\) và \(x\ne7\)