C=\(\frac{x^2-\sqrt{x}}{x+\sqrt{x}+1}-\frac{2x-\sqrt{x}}{\sqrt{x}}+\frac{2\left(x-1\right)}{\sqrt{x}-1}\)
rút gọn
tìm gtnn
tìm x để \(P=\frac{2\sqrt{x}}{C}\) nguyên
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26 tháng 12 2020
\(P=\left(\frac{x\sqrt{x}-1}{x-\sqrt{x}}-\frac{x\sqrt{x}+1}{x+\sqrt{x}}\right):\left(\frac{2\left(x-2\sqrt{x}+1\right)}{x-1}\right)\)
\(=\left[\frac{\left(x\sqrt{x}-1\right)\left(x+\sqrt{x}\right)}{\left(x-\sqrt{x}\right)\left(x+\sqrt{x}\right)}-\frac{\left(x\sqrt{x}+1\right)\left(x-\sqrt{x}\right)}{\left(x-\sqrt{x}\right)\left(x+\sqrt{x}\right)}\right]:\left[\frac{2\left(\sqrt{x}-1\right)^2}{x-1}\right]\)
Phương trình tương đương :
\(=\frac{2x^2-2x}{x^2-x}:\frac{2\left(\sqrt{x}-1\right)^2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)
\(=2:\frac{2\left(\sqrt{x}-1\right)}{\sqrt{x}+1}=\frac{2\left(\sqrt{x}+1\right)}{2\left(\sqrt{x}-1\right)}=\frac{\sqrt{x}+1}{\sqrt{x}-1}\)
30 tháng 4 2019
\(P=\left(\frac{x\sqrt{x}-1}{x-\sqrt{x}}-\frac{x\sqrt{x}+1}{x+\sqrt{x}}\right):\left(\frac{2\left(x-2\sqrt{x}+1\right)}{x-1}\right)\)
ĐKXĐ : \(\hept{\begin{cases}x>0\\x\ne1\end{cases}}\)
a, \(P=\left(\frac{\left(x\sqrt{x}-1\right)\left(x+\sqrt{x}\right)-\left(x\sqrt{x}+1\right)\left(x-\sqrt{x}\right)}{\left(x-\sqrt{x}\right)\left(x+\sqrt{x}\right)}\right):\left(\frac{2\left(\sqrt{x}-1\right)^2}{x-1}\right)\)
\(\Leftrightarrow P=\left(\frac{x^2\sqrt{x}+x^2-x-\sqrt{x}-x^2\sqrt{x}+x^2-x+\sqrt{x}}{x\left(x-1\right)}\right):\left(\frac{2\left(\sqrt{x}-1\right)^2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\right)\)
\(\Leftrightarrow P=\frac{2x\left(x-1\right)\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{2\left(\sqrt{x}-1\right)^2x\left(x-1\right)}\)
\(\Leftrightarrow P=\frac{\sqrt{x}+1}{\sqrt{x}-1}\)
b,\(P=\frac{\sqrt{x}-1+2}{\sqrt{x}-1}\)
Để P thuộc Z
\(\Rightarrow2⋮\sqrt{x}-1\)
\(\Rightarrow\sqrt{x}-1\in\left(1;-1;2;-2\right)\)
\(\Leftrightarrow\sqrt{x}\in\left(2;0;3;-1\right)\)
\(\Leftrightarrow x=0\)(ko t/m đkxđ)
Vậy ko có x nguyên để P nguyên
\(C=\frac{x^2-\sqrt{x}}{x+\sqrt{x}+1}-\frac{2x-\sqrt{x}}{\sqrt{x}}+\frac{2\left(x-1\right)}{\sqrt{x}-1}\) (tự tìm ĐKXĐ)
\(=\frac{\sqrt{x}\left(\sqrt{x}^3-1\right)}{x+\sqrt{x}+1}-\frac{\sqrt{x}\left(2\sqrt{x}-1\right)}{\sqrt{x}}+\frac{2\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}{\sqrt{x}-1}\)
\(=\frac{\sqrt{x}\left(\sqrt{x}-1\right)\left(x+\sqrt{x}+1\right)}{x+\sqrt{x}+1}-\left(2\sqrt{x}-1\right)+2\left(\sqrt{x}+1\right)\)
\(=\sqrt{x}\left(\sqrt{x}-1\right)-2\sqrt{x}+1+2\sqrt{x}+2\)
\(=x-\sqrt{x}+3\)
GTNN:\(x-\sqrt{x}+3=\left(\sqrt{x}-\frac{1}{2}\right)^2+\frac{11}{4}\ge\frac{11}{4}\)
\(\Rightarrow Min\left(C\right)=\frac{11}{4}khi..\sqrt{x}-\frac{1}{2}=0\Leftrightarrow\sqrt{x}=\frac{1}{2}\Leftrightarrow x=\frac{1}{4}\)