cho biểu thức: P=\((\dfrac{x^2 +3x+2}{x^2 +x-2}-\dfrac{x^2-x}{x^2-1}):(\dfrac{1}{x+1}+\dfrac{1}{x-1})\)
a, Rút gọn P
b, tìm x để \(\dfrac{1}{P}-\dfrac{x+1}{8}\)≥1
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7 tháng 11 2021
\(a,P=\left[\dfrac{x+1}{3x\left(x+1\right)}-\dfrac{2x-1}{3x\left(2x-1\right)}-1\right]\cdot\dfrac{2x}{1-x}\left(x\ne1;x\ne-1;x\ne0\right)\\ P=\left(\dfrac{1}{3x}-\dfrac{1}{3x}-1\right)\cdot\dfrac{2x}{1-x}\\ P=-1\cdot\dfrac{2x}{1-x}=\dfrac{2x}{x-1}\\ b,P=2+\dfrac{2}{x-1}\in Z\\ \Leftrightarrow x-1\inƯ\left(2\right)=\left\{-2;-1;1;2\right\}\\ \Leftrightarrow x\in\left\{2;3\right\}\left(x\ne-1;x\ne0\right)\\ c,P\le1\Leftrightarrow\dfrac{2x}{x-1}-1\le0\\ \Leftrightarrow\dfrac{x+1}{x-1}\le0\\ \Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x+1\le0\\x-1>0\end{matrix}\right.\\\left\{{}\begin{matrix}x+1\ge0\\x-1< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow-1\le x< 1\)
7 tháng 11 2021
a: \(P=\left(\dfrac{x+1}{3x\left(x+1\right)}-\dfrac{2x-1}{3x\left(2x-1\right)}-1\right)\cdot\dfrac{2x}{x-1}\)
\(=\dfrac{1-1-3x}{3x}\cdot\dfrac{2x}{x-1}\)
\(=\dfrac{-3x}{3x}\cdot\dfrac{2x}{x-1}=\dfrac{-2x}{x-1}\)
7 tháng 4 2022
a: \(P=\dfrac{x^2-2x+1-x^2-x+3x+1}{\left(x-1\right)\left(x+1\right)}\cdot\dfrac{x^2-1}{2x+1}\)
\(=\dfrac{2}{2x+1}\)
b: Để \(P=\dfrac{3}{x-1}\) thì \(\dfrac{3}{x-1}=\dfrac{2}{2x+1}\)
=>6x+3=2x-2
=>4x=-5
hay x=-5/4
AT
11 tháng 6 2021
a) ĐKXĐ: \(x\ge0,x\ne1\)
\(P=\dfrac{\sqrt{x}}{\sqrt{x}-1}+\dfrac{3}{\sqrt{x}+1}-\dfrac{6\sqrt{x}-4}{x-1}\)
\(=\dfrac{\sqrt{x}}{\sqrt{x}-1}+\dfrac{3}{\sqrt{x}+1}-\dfrac{6\sqrt{x}-4}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)+3\left(\sqrt{x}-1\right)-6\sqrt{x}+4}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\dfrac{x-2\sqrt{x}+1}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}\)
\(=\dfrac{\left(\sqrt{x}-1\right)^2}{\left(\sqrt{x}-1\right)\left(\sqrt{x}+1\right)}=\dfrac{\sqrt{x}-1}{\sqrt{x}+1}\)
b) Để \(P< \dfrac{1}{2}\Rightarrow\dfrac{\sqrt{x}-1}{\sqrt{x}+1}< \dfrac{1}{2}\Rightarrow\dfrac{\sqrt{x}-1}{\sqrt{x}+1}-\dfrac{1}{2}< 0\)
\(\Rightarrow\dfrac{2\sqrt{x}-2-\sqrt{x}-1}{2\sqrt{x}+2}< 0\Rightarrow\dfrac{\sqrt{x}-3}{2\sqrt{x}+2}< 0\)
mà \(2\sqrt{x}+2>0\Rightarrow\sqrt{x}-3< 0\Rightarrow\sqrt{x}< 3\Rightarrow x< 9\)
\(\Rightarrow0\le x< 9\left(x\ne1\right)\)
7 tháng 11 2021
a: \(P=\dfrac{2x-2-3x-3+x+7}{\left(x-1\right)\left(x+1\right)}\cdot\dfrac{\left(x-1\right)\left(x+1\right)}{1-2x}\)
\(=\dfrac{2}{1-2x}\)
7 tháng 11 2021
a: \(P=\dfrac{2x-9-x^2+9+2x^2-4x+x-2}{\left(x-2\right)\left(x-3\right)}=\dfrac{x+1}{x-3}\)
16 tháng 5 2022
a: ĐKXĐ: \(x\notin\left\{0;1;2;3;4;5\right\}\)
b: \(P=\dfrac{1}{\left(x-1\right)\cdot x}+\dfrac{1}{\left(x-2\right)\left(x-1\right)}+\dfrac{1}{\left(x-2\right)\left(x-3\right)}+\dfrac{1}{\left(x-3\right)\left(x-4\right)}+\dfrac{1}{\left(x-4\right)\left(x-5\right)}\)
\(=\dfrac{1}{x-1}-\dfrac{1}{x}+\dfrac{1}{x-2}-\dfrac{1}{x-1}+\dfrac{1}{x-3}-\dfrac{1}{x-2}+\dfrac{1}{x-4}-\dfrac{1}{x-3}+\dfrac{1}{x-5}-\dfrac{1}{x-4}\)
\(=\dfrac{1}{x-5}-\dfrac{1}{x}=\dfrac{x-x+5}{x\left(x-5\right)}=\dfrac{5}{x\left(x-5\right)}\)
22 tháng 2 2021
Sửa đề: \(P=\left(\dfrac{1}{x-\sqrt{x}}+\dfrac{1}{\sqrt{x}-1}\right):\dfrac{\sqrt{x}}{x-2\sqrt{x}+1}\)
a) Ta có: \(P=\left(\dfrac{1}{x-\sqrt{x}}+\dfrac{1}{\sqrt{x}-1}\right):\dfrac{\sqrt{x}}{x-2\sqrt{x}+1}\)
\(=\left(\dfrac{1}{\sqrt{x}\left(\sqrt{x}-1\right)}+\dfrac{\sqrt{x}}{\sqrt{x}\left(\sqrt{x}-1\right)}\right):\dfrac{\sqrt{x}}{\left(\sqrt{x}-1\right)^2}\)
\(=\dfrac{\sqrt{x}+1}{\sqrt{x}\left(\sqrt{x}-1\right)}\cdot\dfrac{\left(\sqrt{x}-1\right)^2}{\sqrt{x}}\)
\(=\dfrac{x-1}{x}\)
b) Sửa đề: \(2\sqrt{x+1}=5\)
Ta có: \(2\sqrt{x+1}=5\)
\(\Leftrightarrow\sqrt{x+1}=\dfrac{5}{2}\)
\(\Leftrightarrow x+1=\dfrac{25}{4}\)
hay \(x=\dfrac{21}{4}\)(thỏa ĐK)
Thay \(x=\dfrac{21}{4}\) vào biểu thức \(P=\dfrac{x-1}{x}\), ta được:
\(P=\left(\dfrac{21}{4}-1\right):\dfrac{21}{4}=\dfrac{17}{4}\cdot\dfrac{4}{21}=\dfrac{17}{21}\)
Vậy: Khi \(2\sqrt{x+1}=5\) thì \(P=\dfrac{17}{21}\)
c) Để \(P>\dfrac{1}{2}\) thì \(P-\dfrac{1}{2}>0\)
\(\Leftrightarrow\dfrac{x-1}{x}-\dfrac{1}{2}>0\)
\(\Leftrightarrow\dfrac{2\left(x-1\right)}{2x}-\dfrac{x-1}{2x}>0\)
mà \(2x>0\forall x\) thỏa mãn ĐKXĐ
nen \(2\left(x-1\right)-x+1>0\)
\(\Leftrightarrow2x-2-x+1>0\)
\(\Leftrightarrow x-1>0\)
hay x>1
Kết hợp ĐKXĐ, ta được: x>1
Vậy: Để \(P>\dfrac{1}{2}\) thì x>1
a: \(P=\left(\dfrac{\left(x+2\right)\left(x+1\right)}{\left(x+2\right)\left(x-1\right)}-\dfrac{x}{x+1}\right):\dfrac{x-1+x+1}{\left(x-1\right)\left(x+1\right)}\)
\(=\left(\dfrac{x+1}{x-1}-\dfrac{x}{x+1}\right)\cdot\dfrac{\left(x-1\right)\left(x+1\right)}{2x}\)
\(=\dfrac{x^2+2x+1-x^2+x}{\left(x-1\right)\left(x+1\right)}\cdot\dfrac{\left(x-1\right)\left(x+1\right)}{2x}=\dfrac{3x+1}{2x}\)
b: 1/P-x+1/8>=1
=>\(\dfrac{2x}{3x+1}-\dfrac{x+1}{8}>=1\)
=>\(\dfrac{16x-3x^2-4x-1-24x-8}{8\left(3x+1\right)}>=0\)
=>\(\dfrac{-3x^2-24x-9}{8\left(3x+1\right)}>=0\)
=>\(\dfrac{x^2+8x+3}{3x+1}< =0\)
TH1: x^2+8x+3<=0 và 3x+1>0
=>x>-1/3 và \(-4-\sqrt{13}< =x< =-4+\sqrt{13}\)
=>Loại
TH2: x^2+8x+3>=0 và 3x+1<0
=>x<-1/3 và (x<=-4-căn 13 hoặc x>=-4+căn 13)
=>x<=-4-căn 13