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![](https://rs.olm.vn/images/avt/0.png?1311)
1, Với \(x\ge0,x\ne1\) ta có :
\(P=\left(\dfrac{1}{\sqrt{x}-1}+\dfrac{\sqrt{x}}{x-1}\right):\left(\dfrac{\sqrt{x}}{\sqrt{x}-1}-1\right)\)
\(=\dfrac{\sqrt{x}+1+\sqrt{x}}{x-1}:\dfrac{\sqrt{x}-\sqrt{x}+1}{\sqrt{x}-1}\)
\(=\dfrac{\left(2\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\)
\(=\dfrac{2\sqrt{x}+1}{\sqrt{x}+1}\)
2, Ta có \(P=\dfrac{7}{4}\)
\(\Rightarrow\dfrac{2\sqrt{x}+1}{\sqrt{x}+1}=\dfrac{7}{4}\)
\(\Leftrightarrow4\left(2\sqrt{x}+1\right)=7\left(\sqrt{x}+1\right)\)
\(\Leftrightarrow8\sqrt{x}+4=7\sqrt{x}=7\)
\(\Leftrightarrow\sqrt{x}=3\)
\(\Leftrightarrow x=9\left(tm\right)\)
1) Ta có: \(P=\left(\dfrac{1}{\sqrt{x}-1}+\dfrac{\sqrt{x}}{x-1}\right):\left(\dfrac{\sqrt{x}}{\sqrt{x}-1}-1\right)\)
\(=\left(\dfrac{\sqrt{x}+1+\sqrt{x}}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\right):\left(\dfrac{\sqrt{x}}{\sqrt{x}-1}-\dfrac{\sqrt{x}-1}{\sqrt{x}-1}\right)\)
\(=\dfrac{2\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\cdot\dfrac{\sqrt{x}-1}{\sqrt{x}-\sqrt{x}+1}\)
\(=\dfrac{2\sqrt{x}+1}{\sqrt{x}+1}\)
2) Để \(P=\dfrac{7}{4}\) thì \(\dfrac{2\sqrt{x}+1}{\sqrt{x}+1}=\dfrac{7}{4}\)
\(\Leftrightarrow4\cdot\left(2\sqrt{x}+1\right)=7\left(\sqrt{x}+1\right)\)
\(\Leftrightarrow8\sqrt{x}+4=7\sqrt{x}+7\)
\(\Leftrightarrow8\sqrt{x}-7\sqrt{x}=7-4\)
\(\Leftrightarrow\sqrt{x}=3\)
hay x=9(nhận)
Vậy: Để \(P=\dfrac{7}{4}\) thì x=9
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,A=2\sqrt{20}-\dfrac{2}{\sqrt{3}+1}-\sqrt{80}+\sqrt{4+2\sqrt{3}}\\ =2.2\sqrt{5}-\dfrac{2\left(\sqrt{3}-1\right)}{\sqrt{3^2}-1}-4\sqrt{5}+\sqrt{\left(\sqrt{3}+1\right)^2}\\ =-\dfrac{2\left(\sqrt{3}-1\right)}{2}+\left|\sqrt{3}+1\right|\\ =-\sqrt{3}+1+\sqrt{3}+1\\ =2\)
\(B=\left(1+\dfrac{x+\sqrt{x}}{1+\sqrt{x}}\right)\left(1+\dfrac{x-\sqrt{x}}{1-\sqrt{x}}\right)\left(dk:x\ge0,x\ne1\right)\\ =\left(1+\dfrac{\sqrt{x}\left(1+\sqrt{x}\right)}{1+\sqrt{x}}\right)\left(1-\dfrac{\sqrt{x}\left(1-\sqrt{x}\right)}{1-\sqrt{x}}\right)\\ =\left(1+\sqrt{x}\right)\left(1-\sqrt{x}\right)\\ =1-x\)
\(b,A=4\sqrt{B}\Leftrightarrow4\sqrt{1-x}=2\\ \Leftrightarrow\sqrt{1-x}=\dfrac{1}{2}\\ \Leftrightarrow\left|1-x\right|=\dfrac{1}{4}\)
\(\Leftrightarrow1-x=\dfrac{1}{4}\\ \Leftrightarrow x=\dfrac{3}{4}\left(tm\right)\)
Vậy \(x=\dfrac{3}{4}\) thì \(A=4\sqrt{B}\).
a) \(A=2\sqrt{20}-\dfrac{2}{\sqrt{3}+1}-\sqrt{80}+\sqrt{4+2\sqrt{3}}\)
\(A=2\cdot2\sqrt{5}-\dfrac{2\left(\sqrt{3}-1\right)}{\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)}-4\sqrt{5}+\sqrt{\left(\sqrt{3}\right)^2+2\sqrt{3}\cdot1+1^2}\)
\(A=4\sqrt{5}-\dfrac{2\left(\sqrt{3}-1\right)}{2}-4\sqrt{5}+\sqrt{\left(\sqrt{3}+1\right)^2}\)
\(A=-\left(\sqrt{3}-1\right)+\sqrt{3}+1\)
\(A=-\sqrt{3}+1+\sqrt{3}+1\)
\(A=2\)
\(B=\left(1+\dfrac{x+\sqrt{x}}{1+\sqrt{x}}\right)\left(1+\dfrac{x-\sqrt{x}}{1-\sqrt{x}}\right)\)
\(B=\left[1+\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)}{\sqrt{x}+1}\right]\left[1-\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)}{\sqrt{x}-1}\right]\)
\(B=\left(1+\sqrt{x}\right)\left(1-\sqrt{x}\right)\)
\(B=1^2-\left(\sqrt{x}\right)^2\)
\(B=1-x\)
b) Ta có: \(A=4\sqrt{B}\)
\(\Rightarrow2=4\sqrt{1-x}\)
\(\Leftrightarrow\sqrt{1-x}=\dfrac{1}{2}\)
\(\Leftrightarrow1-x=\dfrac{1}{4}\)
\(\Leftrightarrow x=1-\dfrac{1}{4}\)
\(\Leftrightarrow x=\dfrac{3}{4}\left(tm\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(A=\dfrac{2x-6\sqrt{x}+x+3\sqrt{x}+3\sqrt{x}+9}{x-9}:\dfrac{2\sqrt{x}-2-\sqrt{x}+3}{\sqrt{x}-3}\)
\(=\dfrac{3x+9}{x-9}\cdot\dfrac{\sqrt{x}-3}{\sqrt{x}+1}=\dfrac{3x+9}{x+4\sqrt{x}+3}\)
b: Để A<-1 thì A+1<0
\(\Leftrightarrow\dfrac{3x+9+x+4\sqrt{x}+3}{x+4\sqrt{x}+3}< 0\)
\(\Leftrightarrow\dfrac{4x+4\sqrt{x}+12}{x+4\sqrt{x}+3}< 0\)
hay \(x\in\varnothing\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(P=\left(\frac{\sqrt{x}}{\sqrt{x}-2}+\frac{4\sqrt{x}-3}{2\sqrt{x}-x}\right):\)\(\left(\frac{\sqrt{x}+2}{\sqrt{x}}-\frac{\sqrt{x}-4}{\sqrt{x}-2}\right)\)
\(=\left(\frac{\sqrt{x}}{\sqrt{x}-2}-\frac{4\sqrt{x}-3}{\sqrt{x}\left(\sqrt{x}-2\right)}\right)\)\(:\left(\frac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-2\right)-\sqrt{x}\left(\sqrt{x}-4\right)}{\sqrt{x}\left(\sqrt{x}-2\right)}\right)\)
\(=\frac{x-4\sqrt{x}+3}{\sqrt{x}\left(\sqrt{x}-2\right)}:\frac{x-4-x+4\sqrt{x}}{\sqrt{x}\left(\sqrt{x}-2\right)}\)
\(=\frac{\left(\sqrt{x}-3\right)\left(\sqrt{x}-1\right)}{\sqrt{x}\left(\sqrt{x}-2\right)}.\frac{\sqrt{x}\left(\sqrt{x}-2\right)}{4\left(\sqrt{x}-1\right)}\)
\(=\frac{\sqrt{x}-3}{4}\)
\(b,\)Để \(P>0\Rightarrow\frac{\sqrt{x}-3}{4}>0\)
Mà \(4>0\Rightarrow\sqrt{x}-3>0\Rightarrow\sqrt{x}>3\Rightarrow x>9\)
\(c,\sqrt{P}_{min}=0\Rightarrow\frac{\sqrt{x}-3}{4}=0\)
\(\Leftrightarrow\sqrt{x}-3=0\Rightarrow\sqrt{x}=3\Rightarrow x=9\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: \(Q=\left(\dfrac{\sqrt{x}+2}{x+2\sqrt{x}+1}-\dfrac{\sqrt{x}-2}{x-1}\right)\cdot\left(x+\sqrt{x}\right)\)
\(=\left(\dfrac{\sqrt{x}+2}{\left(\sqrt{x}+1\right)^2}-\dfrac{\sqrt{x}-2}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\right)\cdot\left(x+\sqrt{x}\right)\)
\(=\dfrac{\left(\sqrt{x}+2\right)\left(\sqrt{x}-1\right)-\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+1\right)^2\cdot\left(\sqrt{x}-1\right)}\cdot\sqrt{x}\cdot\left(\sqrt{x}+1\right)\)
\(=\dfrac{x+\sqrt{x}-2-\left(x-\sqrt{x}-2\right)}{\left(\sqrt{x}+1\right)\cdot\left(\sqrt{x}-1\right)}\cdot\sqrt{x}\)
\(=\dfrac{x+\sqrt{x}-2-x+\sqrt{x}+2}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\cdot\sqrt{x}\)
\(=\dfrac{2\sqrt{x}\cdot\sqrt{x}}{x-1}=\dfrac{2x}{x-1}\)
b: Để Q là số nguyên thì \(2x⋮x-1\)
=>\(2x-2+2⋮x-1\)
=>\(2⋮x-1\)
=>\(x-1\in\left\{1;-1;2;-2\right\}\)
=>\(x\in\left\{2;0;3;-1\right\}\)
Kết hợp ĐKXĐ, ta được: \(x\in\left\{0;2;3\right\}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Đặt \(\left\{{}\begin{matrix}\sqrt{2x+3}=a\ge0\\\sqrt{y}=b\ge0\end{matrix}\right.\)
\(\Rightarrow b\left(b^2+1\right)-3a^2=\left(a^2+1\right)a-3b^2\)
\(\Rightarrow a^3-b^3+3a^2-3b^2+a-b=0\)
\(\Leftrightarrow\left(a-b\right)\left(a^2+ab+b^2\right)+\left(a-b\right)\left(3a+3b\right)+a-b=0\)
\(\Leftrightarrow\left(a-b\right)\left(a^2+ab+b^2+3a+3b+1\right)=0\)
\(\Leftrightarrow a=b\Rightarrow\sqrt{2x+3}=\sqrt{y}\)
\(\Rightarrow y=2x+3\)
\(\Rightarrow M=x\left(2x+3\right)+3\left(2x+3\right)-4x^2-3\) tới đây chắc chỉ cần bấm máy
![](https://rs.olm.vn/images/avt/0.png?1311)
a: Ta có: \(x^2=3-2\sqrt{2}\)
nên \(x=\sqrt{2}-1\)
Thay \(x=\sqrt{2}-1\) vào A, ta được:
\(A=\dfrac{\left(\sqrt{2}+1\right)^2}{\sqrt{2}-1}=\dfrac{3+2\sqrt{2}}{\sqrt{2}-1}=7+5\sqrt{2}\)
\(M=3\left(\sqrt{x}+1\right)^2-\left(\sqrt{x}+4\right)^2+14\)
\(=3\left(x+2\sqrt{x}+1\right)-\left(x+8\sqrt{x}+16\right)+14\)
\(=3x+6\sqrt{x}+3-x-8\sqrt{x}-16+14\)
\(=2x-2\sqrt{x}+1\)
\(=2\left(x-4\sqrt{x}+4\right)+6\sqrt{x}-7\)
\(=2\left(\sqrt{x}-2\right)^2+6\sqrt{x}-7\ge2.0+6.\sqrt{4}-7=5\)
Dấu "=" \(x=4\)
Vậy GTNN của M là 4 <=> x = 4
\(\left\{{}\begin{matrix}xz=x+4\left(1\right)\\2y^2=7xz-3x-14\\x^2+y^2=35-z^2\left(3\right)\end{matrix}\right.\left(2\right)\)
Nhận thấy \(x=0\) không là nghiệm của (1) .
\(\rightarrow z=\dfrac{x+4}{x}\)(4)
Thế (1) vào (2) .
\(2y^2=7\left(x+4\right)-3x-14=4x+14\leftrightarrow y^2=2x+7\)(\(x\ge-\dfrac{7}{2}\)) (5)
Thế (4)(5) vào (3)
\(x^2+2x+7=35-\left(\dfrac{x+4}{x}\right)^2\)
\(\Leftrightarrow x^4+2x^3-27x^2+8x+16=0\)
\(\Leftrightarrow\left(x-4\right)\left(x-1\right)\left(x^2+7x+4\right)=0\)\(\)
TH1 : \(x-4=0\Leftrightarrow x=4\Leftrightarrow\left\{{}\begin{matrix}y=\pm\sqrt{15}\\z=2\end{matrix}\right.\)
TH2 : \(x-1=0\Leftrightarrow x=1\Leftrightarrow\left\{{}\begin{matrix}y=\pm3\\z=5\end{matrix}\right.\)
TH3 : \(x^2+7x+4=0\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-7+\sqrt{33}}{2}\left(TM\right)\\x=\dfrac{-7-\sqrt{33}}{2}\left(KTM\right)\end{matrix}\right.\)
\(\Leftrightarrow x=\dfrac{-7+\sqrt{33}}{2}\Leftrightarrow\left\{{}\begin{matrix}y=\pm\sqrt[4]{33}\\z=-\dfrac{5+\sqrt{33}}{2}\end{matrix}\right.\)