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![](https://rs.olm.vn/images/avt/0.png?1311)
a) đk: \(x\ge0;x\ne1\)
b) \(A=\left(\frac{x+2}{x\sqrt{x}-1}+\frac{\sqrt{x}}{x+\sqrt{x}+1}+\frac{1}{1-\sqrt{x}}\right)\div\frac{\sqrt{x}-1}{2}\)
\(A=\frac{x+2+\left(\sqrt{x}-1\right)\sqrt{x}-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\div\frac{\sqrt{x}-1}{2}\)
\(A=\frac{x+2+x-\sqrt{x}-x-\sqrt{x}-1}{\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}\cdot\frac{2}{\sqrt{x}-1}\)
\(A=\frac{2\left(x-2\sqrt{x}+1\right)}{\left(x-2\sqrt{x}+1\right)\left(x+\sqrt{x}+1\right)}\)
\(A=\frac{2}{x+\sqrt{x}+1}\)
c) Ta có: \(x+\sqrt{x}+1=\left(x+\sqrt{x}+\frac{1}{4}\right)+\frac{3}{4}=\left(\sqrt{x}+\frac{1}{2}\right)^2+\frac{3}{4}\ge\frac{3}{4}>0\)
=> \(\frac{2}{x+\sqrt{x}+1}>0\left(\forall x\ne1\right)\)
d) Ta chỉ có thể tìm GTLN thôi
Để A đạt GTLN => \(x+\sqrt{x}+1\) phải đạt GTNN
Dấu "=" xảy ra khi: \(x=0\)
Vậy Max(A) = 2 khi x = 0
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(A=\dfrac{\sqrt{x}\left(\sqrt{x}-2\right)+2\sqrt{x}\left(\sqrt{x}+2\right)-3x-4}{x-4}\)
\(=\dfrac{x-2\sqrt{x}+2x+4\sqrt{x}-3x-4}{x-4}\)
\(=\dfrac{2\sqrt{x}-4}{x-4}=\dfrac{2}{\sqrt{x}+2}\)
b: A=1/2
=>\(\sqrt{x}+2=4\)
=>\(\sqrt{x}=2\)
=>x=4(loại)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\frac{x\sqrt{x}+26\sqrt{x}-19-2\sqrt{x}\left(\sqrt{x}+3\right)+\left(\sqrt{x}-3\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+3\right)}\)
\(=\frac{x\sqrt{x}+26\sqrt{x}-19-2x-6\sqrt{x}+x-4\sqrt{x}+3}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+3\right)}\)
\(=\frac{x\sqrt{x}-x+16\sqrt{x}-16}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+3\right)}=\frac{x\left(\sqrt{x}-1\right)+16\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+3\right)}\)
\(=\frac{\left(x+16\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+3\right)}=\frac{x+16}{\sqrt{x}+3}\)
+ \(A=\frac{x+16}{\sqrt{x}+3}=\frac{x-9+25}{\sqrt{x}+3}=\frac{\left(\sqrt{x}-3\right)\left(\sqrt{x}+3\right)+25}{\sqrt{x}+3}\) \(=\sqrt{x}-3+\frac{25}{\sqrt{x}+3}\)
\(=\sqrt{x}+3+\frac{25}{\sqrt{x}+3}-6\ge2\sqrt{\left(\sqrt{x}+3\right)\cdot\frac{25}{\sqrt{x}+3}}-6=10-6=4\)
Dấu "=" \(\Leftrightarrow\sqrt{x}+3=\frac{25}{\sqrt{x}+3}\Leftrightarrow\sqrt{x}+3=5\Leftrightarrow x=4\)
Vậy \(A=\frac{x+16}{\sqrt{x}+3}\)
Min A = 4 \(\Leftrightarrow x=4\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1.(√x -2)^2 ≥ 0 --> x -4√x +4 ≥ 0 --> x+16 ≥ 12 +4√x --> (x+16)/(3+√x) ≥4
--> Pmin=4 khi x=4
2. Đặt \(\sqrt{x^2-4x+5}=t\ge1\)1
=> M=2x2-8x+\(\sqrt{x^2-4x+5}\)+6=2(t2-5)+t+6
<=> M=2t2+t-4\(\ge\)2.12+1-4=-1
Mmin=-1 khi t=1 hay x=2
\(A=\frac{x-\sqrt{x}+1}{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}-\frac{3}{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}+\frac{2\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}\)
\(=\frac{x-\sqrt{x}+1-3+2\sqrt{x}+2}{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}=\frac{x+\sqrt{x}}{\left(\sqrt{x}+1\right)\left(x-\sqrt{x}+1\right)}=\frac{\sqrt{x}}{x-\sqrt{x}+1}\)
\(\left\{{}\begin{matrix}\sqrt{x}\ge0\\x-\sqrt{x}+1=\left(\sqrt{x}-\frac{1}{2}\right)^2+\frac{3}{4}>0\end{matrix}\right.\) \(\Rightarrow A\ge0\)
\(\Rightarrow A_{min}=0\) khi \(x=0\)
Với \(x\ne0\Rightarrow A=\frac{1}{\sqrt{x}+\frac{1}{\sqrt{x}}-1}\le\frac{1}{2\sqrt{\sqrt{x}.\frac{1}{\sqrt{x}}}-1}=\frac{1}{2-1}=1\)
\(\Rightarrow A_{max}=1\) khi \(\sqrt{x}=\frac{1}{\sqrt{x}}\Leftrightarrow x=1\)