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a) \(ĐKXĐ:x\ne\pm2\)
\(A=\dfrac{4}{x+2}+\dfrac{2}{x-2}+\dfrac{6-5x}{x^2-4}\)
\(\Leftrightarrow A=\dfrac{4\left(x-2\right)+2\left(x+2\right)+6-5x}{\left(x-2\right)\left(x+2\right)}\)
\(\Leftrightarrow A=\dfrac{4x-8+2x+4+6-5x}{\left(x-2\right)\left(x+2\right)}\)
\(\Leftrightarrow A=\dfrac{x+2}{\left(x-2\right)\left(x+2\right)}\)
\(\Leftrightarrow A=\dfrac{1}{x-2}\)
b) Để A = 1
\(\Leftrightarrow\dfrac{1}{x-2}=1\)
\(\Leftrightarrow x-2=1\)
\(\Leftrightarrow x=3\) (tm)
Vậy ...
c) Để A > 1
\(\Leftrightarrow\dfrac{1}{x-2}>1\)
\(\Leftrightarrow\dfrac{1}{x-2}-1>0\)
\(\Leftrightarrow\dfrac{1-x+2}{x-2}>0\)
\(\Leftrightarrow\dfrac{-x+3}{x-2}>0\)
\(\Leftrightarrow\left(3-x\right)\left(x-2\right)>0\)
Trường hợp \(\left\{{}\begin{matrix}3-x>0\\x-2>0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x< 3\\x>2\end{matrix}\right.\)
\(\Leftrightarrow2< x< 3\) (tm)
Trường hợp \(\left\{{}\begin{matrix}3-x< 0\\x-2< 0\end{matrix}\right.\)
\(\Leftrightarrow\left\{{}\begin{matrix}x>3\\x< 2\end{matrix}\right.\) (ktm)
Vậy ...
d) Để A nguyên
\(\Leftrightarrow\dfrac{1}{x-2}\in Z\)
\(\Leftrightarrow x-2\inƯ\left(1\right)=\left\{\pm1;\pm2\right\}\)
\(\Leftrightarrow x\in\left\{1;3;0;4\right\}\)
Vậy ...
để A xác định
\(\Rightarrow\hept{\begin{cases}x+2\ne0\\x-2\ne0\\x^2\ne4\end{cases}}\Rightarrow x\ne\pm2\)
\(A=\frac{4}{x+2}+\frac{3}{x-2}-\frac{5x-6}{x^2-4}\)
\(A=\frac{4.x-8}{\left(x+2\right).\left(x-2\right)}+\frac{3.x+6}{\left(x-2\right).\left(x+2\right)}-\frac{5x-6}{\left(x-2\right).\left(x+2\right)}\)
\(A=\frac{4x-8+3x+6-5x+6}{\left(x+2\right).\left(x-2\right)}=\frac{2.\left(x+2\right)}{\left(x+2\right).\left(x-2\right)}=\frac{2}{x-2}\)
\(\frac{4}{x+2}+\frac{3}{x-2}-\frac{5x-6}{x^2-4}=\frac{4}{x+2}+\frac{3}{x-2}-\frac{5x-6}{\left(x+2\right)\left(x-2\right)}\)
\(=\frac{4x-8}{\left(x+2\right)\left(x-2\right)}+\frac{3x+4}{\left(x-2\right)\left(x+2\right)}-\frac{5x-6}{\left(x-2\right)\left(x+2\right)}=\frac{4x-8+3x+4-5x+6}{\left(x+2\right)\left(x-2\right)}\)
\(=\frac{2x+2}{\left(x+2\right)\left(x-2\right)}=\frac{2x+2}{x^2-4}\)
C, \(x=4\Rightarrow A=\frac{2x+2}{x^2-4}=\frac{-6}{12}=\frac{-1}{2}\)
d, \(A\inℤ\Leftrightarrow2x+2⋮x^2-4\Leftrightarrow2x^2+2x-2x^2+8⋮x^2-4\Leftrightarrow2x+8⋮x^2-4\)
\(\Leftrightarrow2x^2+8x⋮x^2-4\Leftrightarrow16⋮x^2-4\)
\(x^2-4\inℕ\)
\(\Rightarrow x^2\in\left\{0;4;12\right\}\)
Thử lại thì 12 ko là số chính phương vậy x=0 hoặc x=2 thỏa mãn
mk học lớp 6 mong mn thông cảm nếu có sai sót
\(\frac{x+2}{x+3}-\frac{5}{x^2+x-6}+\frac{1}{2-x}=\frac{x+2}{x+2}+\frac{-5}{x^2+x-6}+\frac{-1}{x-2}\)
=\(\frac{\left(x+2\right)\left(x-2\right)}{x^2+x-6}+\frac{-5}{x^2+x-6}+\frac{-1\left(x+3\right)}{x^2+x-6}=\frac{\left(x+2\right)\left(x-2\right)-5-1\left(x+3\right)}{x^2+x-6}\)
=\(\frac{x^2-4-5-x-3}{x^2+x-6}=\frac{x^2-x-12}{x^2+x+6}\)
\(\frac{x^2-x-12}{x^2+x-6}=\frac{x^2-x-12}{\left(x-2\right)\left(x+3\right)}\)
Để giá trị của PT A được xác định thì \(\left(x-2\right)\ne0\)và \(\left(x+3\right)\ne0\)
=> \(x\ne2\) và \(x\ne-3\) thì PT được xác định
Dài quá trôi hết đề khỏi màn hình: nhìn thấy câu nào giải cấu ấy
Bài 4:
\(A=\frac{\left(x-1\right)+\left(x+1\right)}{\left(x+1\right)\left(x-1\right)}-\frac{2}{\left(x+1\right)\left(x-1\right)}=\frac{2\left(x-1\right)}{\left(x-1\right)\left(x+1\right)}\)
a) DK x khác +-1
b) \(dk\left(a\right)\Rightarrow A=\frac{2}{\left(x+1\right)}\)
c) x+1 phải thuộc Ước của 2=> x=(-3,-2,0))
1. a) Biểu thức a có nghĩa \(\Leftrightarrow\hept{\begin{cases}x+2\ne0\\x^2-4\ne0\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}x+2\ne0\\x-2\ne0\\x+2\ne0\end{cases}}\)
\(\Leftrightarrow\hept{\begin{cases}x\ne-2\\x\ne2\end{cases}}\)
Vậy vs \(x\ne2,x\ne-2\) thì bt a có nghĩa
b) \(A=\frac{x}{x+2}+\frac{4-2x}{\left(x-2\right)\left(x+2\right)}\)
\(=\frac{x\left(x-2\right)}{\left(x+2\right)\left(x-2\right)}+\frac{4-2x}{\left(x+2\right)\left(x-2\right)}\)
\(=\frac{x^2-2x+4-2x}{\left(x+2\right)\left(x-2\right)}\)
\(=\frac{x^2-4x+4}{\left(x+2\right)\left(x-2\right)}\)
\(=\frac{\left(x-2\right)^2}{\left(x+2\right)\left(x-2\right)}\)
\(=\frac{x-2}{x+2}\)
c) \(A=0\Leftrightarrow\frac{x-2}{x+2}=0\)
\(\Leftrightarrow x-2=\left(x+2\right).0\)
\(\Leftrightarrow x-2=0\)
\(\Leftrightarrow x=2\)(ko thỏa mãn điều kiện )
=> ko có gía trị nào của x để A=0
a. \(A=\dfrac{1}{x-1}-\dfrac{1}{x+1}+\dfrac{4x+2}{x^2-1}\)
\(A=\dfrac{x+1}{\left(x-1\right)\left(x+1\right)}-\dfrac{x-1}{\left(x-1\right)\left(x+1\right)}+\dfrac{4x+2}{\left(x-1\right)\left(x+1\right)}\)
\(A=\dfrac{\left(x+1\right)-\left(x-1\right)+4x+2}{\left(x-1\right)\left(x+1\right)}\)
\(A=\dfrac{x+1-x+1+4x+2}{\left(x-1\right)\left(x+1\right)}\)
\(A=\dfrac{4x+4}{\left(x-1\right)\left(x+1\right)}=\dfrac{4\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}=\dfrac{4}{x-1}\)
b) Ta có: \(A=\dfrac{4}{x-1}=\dfrac{4}{2015}\) (ĐK: \(x\ne\pm1\) )
\(\Leftrightarrow8060=4\left(x-1\right)\)
\(\Leftrightarrow8060=4x-4\)
\(\Leftrightarrow8064=4x\)
\(\Leftrightarrow x=\dfrac{8064}{4}=2016\left(tm\right)\)
c) Ta có: \(\dfrac{4}{x-1}\left(x\ne1\right)\)
Để \(\dfrac{4}{x-1}\) nhận giá trị nguyên thì \(4:\left(x-1\right)\Leftrightarrow x-1\in\text{Ư}\left(4\right)=\left\{1;4;2\right\}\)
Vậy với x ∈ {2; 5; 3; 0; -1; -3} thì biểu thức \(\dfrac{4}{x-1}\) nhận giá trị nguyên
d) Thay \(x=-\dfrac{1}{2}\) vào biểu thức A ta được:
\(\dfrac{4}{-\dfrac{1}{2}-1}=-3\)
Vậy biểu thức A có giá trị -3 tại \(x=-\dfrac{1}{2}\)
a: \(A=\dfrac{x^2-2x+2x^2+4x-3x^2-4}{\left(x-2\right)\left(x+2\right)}=\dfrac{2x-4}{\left(x-2\right)\left(x+2\right)}=\dfrac{2}{x+2}\)
a, \(\dfrac{x}{x+2}\) + \(\dfrac{2x}{x-2}\) -\(\dfrac{3x^2-4}{x^2-4}\)
= \(\dfrac{x}{x+2}+\dfrac{2x}{x-2}-\dfrac{3x^2+4}{x^2-4}\)
= \(\dfrac{x}{x+2}+\dfrac{2x}{x-2}-\dfrac{3x^2+4}{\left(x+2\right)\left(x-2\right)}\)
= \(\dfrac{x\left(x-2\right)+2x\left(x+2\right)-3x^2-4}{\left(x+2\right)\left(x-2\right)}\)
= \(\dfrac{2x-4}{\left(x+2\right)\left(x-2\right)}=\dfrac{2\left(x-2\right)}{\left(x+2\right)\left(x-2\right)}=\dfrac{2}{x+2}\)
Có vài bước mình làm tắc á nha :>
\(A=\frac{4}{x+2}+\frac{2}{x-2}+\frac{6-5x}{x^2-4}\)
a) ĐKXĐ : x ≠ ±2
\(=\frac{4\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}+\frac{2\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}+\frac{6-5x}{\left(x-2\right)\left(x+2\right)}\)
\(=\frac{4x-8+2x+4+6-5x}{\left(x-2\right)\left(x+2\right)}=\frac{x+2}{\left(x-2\right)\left(x+2\right)}=\frac{1}{x-2}\)
b) Để A = 1 => \(\frac{1}{x-2}=1\)=> x - 2 = 1 => x = 3 ( tm )
c) Để A > 1 => \(\frac{1}{x-2}>1\)
=> \(\frac{1}{x-2}-1>0\)
=> \(\frac{1}{x-2}-\frac{x-2}{x-2}>0\)
=> \(\frac{1-x+2}{x-2}>0\)
=> \(\frac{-x+3}{x-2}>0\)
Xét hai trường hợp
1. \(\hept{\begin{cases}-x+3>0\\x-2>0\end{cases}}\Rightarrow\hept{\begin{cases}-x>-3\\x>2\end{cases}}\Rightarrow\hept{\begin{cases}x< 3\\x>2\end{cases}}\Rightarrow2< x< 3\)
2. \(\hept{\begin{cases}-x+3< 0\\x-2< 0\end{cases}}\Rightarrow\hept{\begin{cases}-x< -3\\x< 2\end{cases}}\Rightarrow\hept{\begin{cases}x>3\\x< 2\end{cases}}\)( loại )
Vậy với 2 < x < 3 thì A > 1
d) Để A nguyên => \(\frac{1}{x-2}\)nguyên
=> 1 ⋮ x - 2
=> x - 2 ∈ Ư(1) = { ±1 }
=> x ∈ { 1 ; 3 } thì A nguyên