1.cho biểu thức
|D=(1/x-1-x/1-x^3-x^2+x+1/x+1):2x+1/x^2+x+1)
a)rút gọn D
b)tính gtri của D
c)tìm gtri nguyên của x để biểu thức D có gtri nguyên
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27 tháng 10 2021
Bài 1:
a: \(Q=\left(\dfrac{\sqrt{x}+2}{x+2\sqrt{x}+1}-\dfrac{\sqrt{x}-2}{x-1}\right)\left(x+\sqrt{x}\right)\)
\(=\dfrac{x+\sqrt{x}-2-x+\sqrt{x}+2}{\left(\sqrt{x}+1\right)^2\cdot\left(\sqrt{x}-1\right)}\cdot\sqrt{x}\left(\sqrt{x}+1\right)\)
\(=\dfrac{2x}{x-1}\)
AT
1 tháng 6 2018
a/ ĐKXĐ: x khác -1
\(P=\left(\dfrac{4}{x+1}-1\right):\dfrac{9-x^2}{x^2+2x+1}=\left(\dfrac{4}{x+1}-\dfrac{x+1}{x+1}\right)\cdot\dfrac{\left(x+1\right)^2}{\left(3-x\right)\left(3+x\right)}\)
\(=\dfrac{3-x}{x+1}\cdot\dfrac{\left(x+1\right)^2}{\left(3-x\right)\left(3+x\right)}=\dfrac{x+1}{x+3}\)
b/ |x + 1| = 2
\(\Leftrightarrow\left[{}\begin{matrix}x+1=2\\x+1=-2\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=1\left(tm\right)\\x=-3\left(ktm\right)\end{matrix}\right.\)
Với x = 1 P = \(\dfrac{1+1}{1+3}=\dfrac{2}{4}=\dfrac{1}{2}\)
c/ \(\dfrac{x+1}{x+3}=\dfrac{x+3-2}{x+3}=\dfrac{x+3}{x+3}-\dfrac{2}{x+3}=1-\dfrac{2}{x+3}\)
ĐỂ P nguyên thì \(\dfrac{2}{x+3}\in Z\Leftrightarrow x+3\inƯ\left(2\right)\)
\(x+3=\left\{-2;-1;1;2\right\}\)
=> \(x=\left\{-5;-4;-2;-1\right\}\) (tm)
Vậy............
VD
21 tháng 3 2022
\(B=\dfrac{\sqrt{x}}{\sqrt{x}-1}-\dfrac{2\sqrt{x}}{x-1}-\dfrac{1}{\sqrt{x}+1}\\ =\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}-\dfrac{2\sqrt{x}}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}-\dfrac{\sqrt{x}-1}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\\ =\dfrac{x+\sqrt{x}-2\sqrt{x}-\sqrt{x}+1}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\\ =\dfrac{x-2\sqrt{x}+1}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\\ =\dfrac{\left(\sqrt{x}-1\right)^2}{\left(\sqrt{x}+1\right)\left(\sqrt{x}-1\right)}\\ =\dfrac{\sqrt{x}-1}{\sqrt{x}+1}\)
Thay \(x=6-2\sqrt{5}\) vào B ta có:
\(B=\dfrac{\sqrt{x}-1}{\sqrt{x}+1}\\ =\dfrac{\sqrt{6-2\sqrt{5}}-1}{\sqrt{6-2\sqrt{5}}+1}\\ =\dfrac{\sqrt{5-2\sqrt{5}+1}-1}{\sqrt{5-2\sqrt{5}+1}+1}\\ =\dfrac{\sqrt{\left(\sqrt{5}-1\right)^2}-1}{\sqrt{\left(\sqrt{5}-1\right)^2}+1}\\ =\dfrac{\sqrt{5}-1-1}{\sqrt{5}-1+1}\\ =\dfrac{\sqrt{5}-2}{\sqrt{5}}\\ =\dfrac{\sqrt{5}\left(\sqrt{5}-2\right)}{5}\\ =\dfrac{5-2\sqrt{5}}{5}\)
4 tháng 12 2017
a, Để C có nghĩa <=> \(\left\{{}\begin{matrix}2x-2\ne0\\2-2x^2\ne0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}2x\ne2\\2x^2\ne2\end{matrix}\right.\)\(\Leftrightarrow\left\{{}\begin{matrix}x\ne1\\x\ne-1\end{matrix}\right.\)\(\Leftrightarrow x\ne\pm1\) thì C có nghĩa.
b, \(\dfrac{x}{2x-2}+\dfrac{x^2+1}{2-2x^2}=\dfrac{x}{2\left(x-1\right)}+\dfrac{-\left(x^2+1\right)}{2\left(x^2-1\right)}\)
\(=\dfrac{x}{2\left(x-1\right)}+\dfrac{-\left(x^2+1\right)}{2\left(x-1\right)\left(x+1\right)}\)
\(=\dfrac{x\left(x+1\right)}{2\left(x-1\right)\left(x+1\right)}+\dfrac{-\left(x^2+1\right)}{2\left(x-1\right)\left(x+1\right)}\)
\(=\dfrac{x^2+x-x^2-1}{2\left(x-1\right)\left(x+1\right)}=\dfrac{x-1}{2\left(x-1\right)\left(x+1\right)}=\dfrac{1}{2\left(x+1\right)}\)
c, \(C=-0,5\Leftrightarrow\dfrac{1}{2\left(x+1\right)}=-0,5\)
\(\Leftrightarrow2\left(x+1\right)=\dfrac{1}{-0,5}=-2\Leftrightarrow x+1=-1\Leftrightarrow x=-2\)
Vậy....
12 tháng 12 2017
ĐKXĐ : \(\left\{{}\begin{matrix}x-3\ne0\\x+3\ne0\\9-x^2\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x\ne3\\x\ne-3\end{matrix}\right.\)
a, \(A=\dfrac{x-5}{x-3}-\dfrac{2x}{x+3}-\dfrac{2x^2-x+15}{9-x^2}\)
\(=\dfrac{\left(x-5\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}-\dfrac{2x\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}+\dfrac{2x^2-x+15}{\left(x-3\right)\left(x+3\right)}\)
\(=\dfrac{x^2-2x-15-2x^2+6x+2x^2-x+15}{\left(x-3\right)\left(x+3\right)}\)
\(=\dfrac{x^2-3x}{\left(x-3\right)\left(x+3\right)}\)
\(=\dfrac{x\left(x-3\right)}{\left(x-3\right)\left(x+3\right)}=\dfrac{x}{x+3}\)
b, \(\left|x-1\right|=2\)
\(\Rightarrow\left[{}\begin{matrix}x-1=2\\x-1=-2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\left(kot/m\right)\\x=-1\left(t/m\right)\end{matrix}\right.\)
Thay x =- 1 vào biểu thức A ,có :
\(\dfrac{-1}{-1+3}=\dfrac{-1}{2}\)
Vậy tại x = -1 gtri của bt A là -1/2
Vậy tại x = 3 biểu thức A ko có giá trị
c,\(\dfrac{x}{x+3}=\dfrac{x+3-3}{x+3}=1-\dfrac{3}{x+3}\)
Để A có giá trị nguyên
\(\Leftrightarrow\dfrac{3}{x+3}\) là số nguyên
\(\Leftrightarrow3⋮x+3\)
\(\Leftrightarrow x+3\inƯ\left(3\right)=\left\{1;-1;3;-3\right\}\)
| \(x+3\) | 1 | -1 | 3 | -3 |
| x | -2 (t/m) | -4(t/m) | 0 (t/m) | -6(t/m) |
Vậy \(x\in\left\{0;-2;-4;-6\right\}\) thì A có giá trị nguyên
