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Bài 1: ĐKXĐ:`x + 3 ne 0` và `x^2+ x-6 ne 0 ; 2-x ne 0`
`<=> x ne -3 ; (x-2)(x+3) ne 0 ; x ne2`
`<=>x ne -3 ; x ne 2`
b) Với `x ne - 3 ; x ne 2` ta có:
`P= (x+2)/(x+3) - 5/(x^2 +x -6) + 1/(2-x)`
`P = (x+2)/(x+3) - 5/[(x-2)(x+3)] + 1/(2-x)`
`= [(x+2)(x-2)]/[(x-2)(x+3)] - 5/[(x-2)(x+3)] - (x+3)/[(x-2)(x+3)]`
`= (x^2 -4)/[(x-2)(x+3)] - 5/[(x-2)(x+3)] - (x+3)/[(x-2)(x+3)]`
`=(x^2 - 4 - 5 - x-3)/[(x-2)(x+3)]`
`= (x^2 - x-12)/[(x-2)(x+3)]`
`= [(x-4)(x+3)]/[(x-2)(x+3)]`
`= (x-4)/(x-2)`
Vậy `P= (x-4)/(x-2)` với `x ne -3 ; x ne 2`
c) Để `P = -3/4`
`=> (x-4)/(x-2) = -3/4`
`=> 4(x-4) = -3(x-2)`
`<=>4x -16 = -3x + 6`
`<=> 4x + 3x = 6 + 16`
`<=> 7x = 22`
`<=> x= 22/7` (thỏa mãn ĐKXĐ)
Vậy `x = 22/7` thì `P = -3/4`
d) Ta có: `P= (x-4)/(x-2)`
`P= (x-2-2)/(x-2)`
`P= 1 - 2/(x-2)`
Để P nguyên thì `2/(x-2)` nguyên
`=> 2 vdots x-2`
`=> x -2 in Ư(2) ={ 1 ;2 ;-1;-2}`
+) Với `x -2 =1 => x= 3` (thỏa mãn ĐKXĐ)
+) Với `x -2 =2 => x= 4` (thỏa mãn ĐKXĐ)
+) Với `x -2 = -1=> x= 1` (thỏa mãn ĐKXĐ)
+) Với `x -2 = -2 => x= 0`(thỏa mãn ĐKXĐ)
Vậy `x in{ 3 ;4; 1; 0}` thì `P` nguyên
e) Từ `x^2 -9 =0`
`<=> (x-3)(x+3)=0`
`<=> x= 3` hoặc `x= -3`
+) Với `x=3` (thỏa mãn ĐKXĐ) thì:
`P = (3-4)/(3-2)`
`P= -1/1`
`P=-1`
+) Với `x= -3` thì không thỏa mãn ĐKXĐ
Vậy với x= 3 thì `P= -1`
a: ĐKXĐ: x<>1; x<>2; x<>-2; x<>-1
\(P=\dfrac{2017x+2017-2016x+2016-2014x-2016}{\left(x-1\right)\left(x+1\right)}\cdot\dfrac{\left(x-1\right)\left(x+1\right)}{\left(x-2\right)\left(x+2\right)}\)
\(=\dfrac{-2015x+2017}{x^2-4}\)
a: \(A=\dfrac{x+2+x^2-2x+x-2}{\left(x-2\right)\left(x+2\right)}=\dfrac{x^2}{x^2-4}\)
a: \(A=\dfrac{x+2+x^2-2x+x-2}{\left(x-2\right)\left(x+2\right)}=\dfrac{x^2-2x}{\left(x-2\right)\left(x+2\right)}=\dfrac{x}{x+2}\)
a) \(A=\dfrac{x+2+x^2-2x+1}{\left(x-2\right)\left(x+2\right)}=\dfrac{x^2-x+1}{\left(x-2\right)\left(x+2\right)}\)
a: \(A=\dfrac{x+2+x^2-2x+x-2}{\left(x+2\right)\left(x-2\right)}=\dfrac{x^2}{x^2-4}\)
\(a,P=\dfrac{2x^2+2x+2+2x-1+x^2+6x+2}{\left(x-1\right)\left(x^2+x+1\right)}\\ P=\dfrac{3x^2+10x+3}{\left(x-1\right)\left(x^2+x+1\right)}\)
a) đk x khác 0;2
P = \(\dfrac{1}{x\left(x-2\right)}.\left(\dfrac{x^2+4}{x}-4\right)+1\)
= \(\dfrac{1}{x\left(x-2\right)}.\dfrac{x^2-4x+4}{x}+1\)
= \(\dfrac{1}{x\left(x-2\right)}.\dfrac{\left(x-2\right)^2}{x}+1\)
= \(\dfrac{x-2}{x^2}+1\)
= \(\dfrac{x^2+x-2}{x^2}\)
b) Để \(\left|2+x\right|=1\)
<=> \(\left[{}\begin{matrix}2+x=1< =>x=-1\left(tm\right)\\2+x=-1< =>x=-3\left(tm\right)\end{matrix}\right.\)
TH1: x = -1
Thay x = -1 vào P, ta có:
\(P=\dfrac{\left(-1\right)^2-1-2}{\left(-1\right)^2}=-2\)
TH2: x = -3
Thay x = -3 vào P, ta có:
\(P=\dfrac{\left(-3\right)^2-3-2}{\left(-3\right)^2}=\dfrac{4}{9}\)
c) P = \(1+\dfrac{x-2}{x^2}\)
Xét \(\dfrac{x^2}{x-2}=\dfrac{\left(x-2\right)^2+4\left(x-2\right)+4}{x-2}\)
= \(\left(x-2\right)+\dfrac{4}{x-2}+4\)
Áp dụng bdt co-si, ta có:
\(\left(x-2\right)+\dfrac{4}{x-2}\ge2\sqrt{\left(x-2\right)\dfrac{4}{x-2}}=4\)
<=> \(\dfrac{x^2}{x-2}\ge4+4=8\)
<=> \(\dfrac{x-2}{x^2}\le\dfrac{1}{8}\)
<=> A \(\le\dfrac{9}{8}\)
Dấu "=" <=> x = 4
a: \(B=\dfrac{x^2-1-2x+3x+1}{x\left(x-1\right)}=\dfrac{x^2+x}{x\left(x-1\right)}=\dfrac{x+1}{x-1}\)
a) B = \(\dfrac{x+1}{x}-\dfrac{2}{x-1}+\dfrac{3x+1}{x\left(x-1\right)}\) (ĐK: \(x\ne0;1\))
= \(\dfrac{\left(x+1\right)\left(x-1\right)}{x\left(x-1\right)}-\dfrac{2x}{x\left(x-1\right)}+\dfrac{3x+1}{x\left(x-1\right)}\)
= \(\dfrac{x^2-1-2x+3x+1}{x\left(x-1\right)}=\dfrac{x^2+x}{x\left(x-1\right)}=\dfrac{x+1}{x-1}\)
b) \(\left|x\right|=1< =>\left[{}\begin{matrix}x=1\left(L\right)\\x=-1\left(C\right)\end{matrix}\right.\)
Thay x = -1 vào B, ta có:
\(\dfrac{-1+1}{-1-1}=0\)
c) B nguyên <=> \(\dfrac{x+1}{x-1}\) nguyên <=> \(1+\dfrac{2}{x-1}\) nguyên
<=> 2\(⋮x-1\)
<=> x-1 \(\in\left\{-2;-1;1;2\right\}\)
| x-1 | -2 | -1 | 1 | 2 |
| x | -1 | 0 | 2 | 3 |
| C | L | C | C |
KL: x \(\in\left\{-1;2;3\right\}\)
\(a,\dfrac{x+1}{x-1}-\dfrac{x-1}{x+1}+\dfrac{4}{1-x^2}\\ =\dfrac{\left(x+1\right)^2}{\left(x-1\right)\left(x+1\right)}-\dfrac{\left(x-1\right)^2}{\left(x+1\right)\left(x-1\right)}-\dfrac{4}{\left(x-1\right)\left(x+1\right)}\\ =\dfrac{x^2+2x+1-x^2+2x-1-4}{\left(x-1\right)\left(x+1\right)}\\ =\dfrac{4x-4}{\left(x-1\right)\left(x+1\right)}\\ =\dfrac{4\left(x-1\right)}{\left(x-1\right)\left(x+1\right)}\\ =\dfrac{4}{x+1}\)
b, \(P=2022\)
\(\Leftrightarrow\dfrac{4}{x+1}=2022\\ \Leftrightarrow4=2022x+2022\\ \Leftrightarrow2022x=-2018\\ \Leftrightarrow x=-\dfrac{1009}{1011}\)
c, P nguyên
\(\Leftrightarrow\dfrac{4}{x+1}\in Z\\ \Rightarrow4⋮\left(x+1\right)\\ \Rightarrow x+1\inƯ\left(4\right)\)
Ta có bảng:
Vậy \(x\in\left\{-5;-3;-2;0;3\right\}\)