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a)B = \(\dfrac{2x}{x+3}+\dfrac{x+1}{x-3}+\dfrac{7x+3}{9-x^2}\left(ĐK:x\ne\pm3\right)\)
= \(\dfrac{2x}{x+3}+\dfrac{x+1}{x-3}-\dfrac{7x+3}{x^2-9}\)
= \(\dfrac{2x\left(x-3\right)+\left(x+1\right)\left(x+3\right)-7x-3}{\left(x+3\right)\left(x-3\right)}\)
= \(\dfrac{3x^2-9x}{\left(x+3\right)\left(x-3\right)}=\dfrac{3x}{x+3}\)
b) \(\left|2x+1\right|=7< =>\left[{}\begin{matrix}2x+1=7< =>x=3\left(L\right)\\2x+1=-7< =>x=-4\left(C\right)\end{matrix}\right.\)
Thay x = -4 vào B, ta có:
B = \(\dfrac{-4.3}{-4+3}=12\)
c) Để B = \(\dfrac{-3}{5}\)
<=> \(\dfrac{3x}{x+3}=\dfrac{-3}{5}< =>\dfrac{3x}{x+3}+\dfrac{3}{5}=0\)
<=> \(\dfrac{15x+3x+9}{5\left(x+3\right)}=0< =>x=\dfrac{-1}{2}\left(TM\right)\)
d) Để B nguyên <=> \(\dfrac{3x}{x+3}\) nguyên
<=> \(3-\dfrac{9}{x+3}\) nguyên <=> \(9⋮x+3\)
| x+3 | -9 | -3 | -1 | 1 | 3 | 9 |
| x | -12(C) | -6(C) | -4(C) | -2(C) | 0(C) | 6(C) |
a: \(B=\dfrac{3x\left(2x-3\right)-4\left(2x+3\right)-4x^2+23x+12}{\left(2x-3\right)\left(2x+3\right)}\cdot\dfrac{2x+3}{x+3}\)
\(=\dfrac{6x^2-9x-8x-12-4x^2+23x+12}{2x-3}\cdot\dfrac{1}{x+3}\)
\(=\dfrac{2x^2+6x}{\left(2x-3\right)}\cdot\dfrac{1}{x+3}=\dfrac{2x}{2x-3}\)
b: 2x^2+7x+3=0
=>(2x+3)(x+2)=0
=>x=-3/2(loại) hoặc x=-2(nhận)
Khi x=-2 thì \(A=\dfrac{2\cdot\left(-2\right)}{-2-3}=\dfrac{-4}{-7}=\dfrac{4}{7}\)
d: |B|<1
=>B>-1 và B<1
=>B+1>0 và B-1<0
=>\(\left\{{}\begin{matrix}\dfrac{2x+2x-3}{2x-3}>0\\\dfrac{2x-2x+3}{2x-3}< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2x-3< 0\\\dfrac{4x-3}{2x-3}>0\end{matrix}\right.\Leftrightarrow x< \dfrac{3}{4}\)
a: \(\Leftrightarrow3x^3-2x^2+15x^2-10x+3x-2+7⋮3x-2\)
\(\Leftrightarrow3x-2\in\left\{1;-1;7;-7\right\}\)
hay \(x\in\left\{3;1\right\}\)
b: \(\Leftrightarrow2x^5-7x^3+4x^4-14x^2+14x^2-49x+49x-44⋮2x^2-7\)
\(\Leftrightarrow2401x^2-1936⋮2x^2-7\)
\(\Leftrightarrow4802x^2-3872⋮2x^2-7\)
\(\Leftrightarrow2x^2-7\inƯ\left(12935\right)\)
\(\Leftrightarrow2x^2-7\in\left\{1;5;13;65;199;995;2587;12935;-1;-5\right\}\)
\(\Leftrightarrow2x^2\in\left\{8;72;2\right\}\)
hay \(x\in\left\{2;-2;6;-6;1;-1\right\}\)
a: Để C là số nguyên thì \(3x^3+6x^2+3x+x^2+2x+1-2⋮x^2+2x+1\)
=>\(x^2+2x+1\in\left\{1;-1;2;-2\right\}\)
=>(x+1)^2=1 hoặc (x+1)^2=2
=>\(x\in\left\{0;-2;\sqrt{2}-1;-\sqrt{2}-1\right\}\)
b: Để D là số nguyên thì \(x^4+x^2+x^3+x-29⋮x^2+1\)
=>\(x^2+1\in\left\{1;-1;29;-29\right\}\)
=>x^2+1=1 hoặc x^2+1=29
=>\(x\in\left\{0;2\sqrt{7};-2\sqrt{7}\right\}\)
a) ta có: A=\(\frac{21x+3}{7x+1}=\frac{3\left(7x+1\right)}{7x+1}=3\) với x khác -1/7
Vâỵ vs mọi gt trị của x thuộc Z (x khác -1/7) thì A mang gt nguyên
b)ta có: B=\(\frac{3x+2}{2x+3}\) => 2B=\(\frac{3\left(2x+3\right)-5}{2x+3}=3-\frac{5}{2x+3}\)
để B có giá trị nguyên <=>2B có gt nguyên <=> \(\frac{5}{2x+3}\) có gt nguyên<=> 2x+3 là các ước nguyên của 5
Ư(5)={-5 ; -1 ; 1 ; 5}
ta có bảng:
| 2x+3 | -5 | -1 | 1 | 5 |
| x | -4 | -2 | -1 | 1 |
Vậy với x={-4 ; -2 ; -1 ; 1} thì B nguyên
\(a,A=\dfrac{x^2-6x+9-x^2+9}{x\left(x-3\right)}\cdot\dfrac{x}{2\left(x-1\right)}\\ A=\dfrac{-6x+18}{2\left(x-3\right)\left(x-1\right)}=\dfrac{-6\left(x-3\right)}{2\left(x-3\right)\left(x-1\right)}=\dfrac{-3}{x-1}\\ b,A\in Z\Leftrightarrow x-1\inƯ\left(-3\right)=\left\{-3;-1;1;3\right\}\\ \Leftrightarrow x\in\left\{-2;0;2;4\right\}\)
a: Để A là số nguyên thì
x^3-2x^2+4 chia hết cho x-2
=>\(x-2\in\left\{1;-1;2;-2;4;-4\right\}\)
=>\(x\in\left\{3;1;4;0;6;-2\right\}\)
b: Để B là số nguyên thì
\(3x^3-x^2-6x^2+2x+9x-3+2⋮3x-1\)
=>\(3x-1\in\left\{1;-1;2;-2\right\}\)
=>\(x\in\left\{\dfrac{2}{3};0;1;-\dfrac{1}{3}\right\}\)
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)
ĐKXĐ: \(x\ne-4\)
Để A nguyên thì \(3x+21⋮x+4\)
\(\Leftrightarrow3x+12+9⋮x+4\)
mà \(3x+12⋮x+4\)
nên \(9⋮x+4\)
\(\Leftrightarrow x+4\inƯ\left(9\right)\)
\(\Leftrightarrow x+4\in\left\{1;-1;3;-3;9;-9\right\}\)
\(\Leftrightarrow x\in\left\{-3;-5;-1;-7;5;-13\right\}\)(nhận)
Vậy: Để A nguyên thì \(x\in\left\{-3;-5;-1;-7;5;-13\right\}\)
b) ĐKXĐ: \(x\ne\dfrac{1}{2}\)
Để B nguyên thì \(2x^3-7x^2+7x+5⋮2x-1\)
\(\Leftrightarrow2x^3-x^2-6x^2+3x+4x-2+7⋮2x-1\)
\(\Leftrightarrow x^2\left(2x-1\right)-3x\left(2x-1\right)+2\left(2x-1\right)+7⋮2x-1\)
\(\Leftrightarrow\left(2x-1\right)\left(x^2-3x+2\right)+7⋮2x-1\)
mà \(\left(2x-1\right)\left(x^2-3x+2\right)⋮2x-1\)
nên \(7⋮2x-1\)
\(\Leftrightarrow2x-1\inƯ\left(7\right)\)
\(\Leftrightarrow2x-1\in\left\{1;-1;7;-7\right\}\)
\(\Leftrightarrow2x\in\left\{2;0;8;-6\right\}\)
hay \(x\in\left\{1;0;4;-3\right\}\)(nhận)
Vậy: \(x\in\left\{1;0;4;-3\right\}\)