Bài 1)

\(\dfrac{9}{12}+\dfrac{10}{12}=\dfrac{12}{19}\)

\(\dfrac{50}{54}=\dfrac{27}{25}\)

\(\dfrac{16}{24}-\dfrac{9}{24}=\dfrac{7}{24}\)

\(\dfrac{8}{5}x\dfrac{4}{3}=\dfrac{32}{15}\)

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Bài 2)

a) \(x=\dfrac{5}{2}-\dfrac{2}{7}\)

\(x=\dfrac{31}{14}\)

b) \(x=\dfrac{6}{7}x\dfrac{4}{5}\)

\(x=\dfrac{24}{35}\)

bài 1.

a , =19/12

b, =25/27

c, = 7/24

d, = 32/15

bài 2:

a:

x=5/2 - 2/7

x=31/14

b:

x=6/7 x 4/5

x=24/35

Bài 6:

a: Ta có: \(E=1:\left(\dfrac{x^2+2}{x^3-1}-\dfrac{x+1}{x^2+x+1}-\dfrac{x+1}{x^2-1}\right)\)

\(=1:\left(\dfrac{x^2+2}{\left(x-1\right)\left(x^2+x+1\right)}-\dfrac{x+1}{x^2+x+1}-\dfrac{1}{x-1}\right)\)

\(=1:\dfrac{x^2+2-x^2+1-x^2-x-1}{\left(x-1\right)\left(x^2+x+1\right)}\)

\(=\dfrac{\left(x-1\right)\left(x^2+x+1\right)}{-x^2-x+2}\)

\(=\dfrac{-\left(x-1\right)\left(x^2+x+1\right)}{\left(x+2\right)\left(x-1\right)}\)

\(=\dfrac{-x^2-x-1}{x+2}\)

cảm ơn nhá

a. ĐKXĐ: \(x\ge4\)

\(F=\left(\dfrac{2+x}{2-x}-\dfrac{4x^2}{x^2-4}-\dfrac{2-x}{2+x}\right):\dfrac{x^2-3x}{2x^2-x^3}\)

\(=\left(\dfrac{\left(2+x\right)\left(2+x\right)}{\left(2-x\right)\left(2+x\right)}+\dfrac{4x^2}{\left(2-x\right)\left(2+x\right)}-\dfrac{\left(2-x\right)\left(2-x\right)}{\left(2-x\right)\left(2+x\right)}\right):\dfrac{x\left(x-3\right)}{x^2\left(2-x\right)}\)

\(=\dfrac{4+4x+x^2+4x^2-4+4x-x^2}{\left(2-x\right)\left(2+x\right)}.\dfrac{x^2\left(2-x\right)}{x\left(x-3\right)}\)

\(=\dfrac{4x^2+8x}{\left(2-x\right)\left(2+x\right)}.\dfrac{x^2\left(2-x\right)}{x\left(x-3\right)}=\dfrac{4x\left(x+2\right)x^2\left(2-x\right)}{\left(x+2\right)\left(2-x\right)x\left(x-3\right)}=\dfrac{4x^2}{x-3}\)

b. Ta có \(\left|x-5\right|=2\) \(\Leftrightarrow\left[{}\begin{matrix}x-5=2\\5-x=2\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=7\\x=3\end{matrix}\right.\)

* Với \(x=7\), ta có biểu thức \(F=\dfrac{4.7^2}{7-3}=\dfrac{196}{4}=49\)

* Với \(x=3\), ta có biểu thức \(F=\dfrac{4.3^2}{3-3}=\dfrac{36}{0}\), lúc này biểu thức không xác định 

c. \(F>0\Leftrightarrow\dfrac{4x^2}{x-3}>0\), vì \(4x^2\ge0\forall x\) nên để \(\dfrac{4x^2}{x-3}>0\)  thì \(\left\{{}\begin{matrix}4x^2>0\\x-3>0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x>0\\x>3\end{matrix}\right.\) \(\Leftrightarrow x>3\)

\(4x^2>0\) thì không tương đương với \(x>0\) mà tương đương với \(x\ne0\)

1.B

2.A

3.B

4.C

5.B

6.D

7.C

8.D

9.B

10.A

mik xin chân thành cảm ơn bn nha!

\(B=|2014-2x|+|2016-2x|\)

\(=|2014-2x|+|2x-2016|\ge|2014-2x+2x-2016|\)

Hay \(B\ge2\)

Dấu"="xảy ra \(\Leftrightarrow\left(2014-2x\right)\left(2x-2016\right)\ge0\)

\(\Leftrightarrow\hept{\begin{cases}2014-2x\ge0\\2x-2016\ge0\end{cases}}\)hoặc \(\hept{\begin{cases}2014-2x< 0\\2x-2016< 0\end{cases}}\)

\(\Leftrightarrow\hept{\begin{cases}2x\le2014\\2x\ge2016\end{cases}\left(loai\right)}\)hoặc\(\hept{\begin{cases}2x>2014\\2x< 2016\end{cases}}\) 

\(\Leftrightarrow\hept{\begin{cases}x>1007\\x< 1008\end{cases}}\)

\(\Leftrightarrow1007< x< 1008\)

Vậy \(B_{min}=2\)\(\Leftrightarrow1007< x< 1008\)

Lời giải:

a.

\(G=\frac{x^2-4}{x+1}+\frac{2}{x+1}:\frac{(2x-3)(x+1)-(2x+1)(x-1)}{(x-1)(x+1)}\)

\(=\frac{x^2-4}{x+1}+\frac{2}{x+1}:\frac{-2}{(x-1)(x+1)}=\frac{x^2-4}{x+1}+\frac{2}{x+1}.\frac{(x+1)(x-1)}{-2}\)

\(=\frac{x^2-4}{x+1}-(x-1)=\frac{x^2-4-(x^2-1)}{x+1}=\frac{-3}{x+1}\)

b.

Để $A\in\mathbb{Z}^+$ thì $x+1$ là ước âm của $-3$

$\Rightarrow x+1\in\left\{-1;-3\right\}$

$\Leftrightarrow x\in\left\{-2;-4\right\}$ (tm)

c.

$G< -1\Leftrightarrow \frac{-3}{x+1}+1< 0$

$\Leftrightarrow \frac{x-2}{x+1}< 0$

$\Leftrightarrow x-2<0< x+1$ hoặc $x-2>0>x+1$

$\Leftrightarrow -1< x< 2$ (chọn) hoặc $-1> x>2$ (loại)

Vậy $-1< x< 2$ và $x\neq 1$

Bài 8:

a: Ta có: \(G=\dfrac{x^2-4}{x+1}+\dfrac{2}{x+1}:\left(\dfrac{2x-3}{x-1}-\dfrac{2x+1}{x+1}\right)\)

\(=\dfrac{x^2-4}{x+1}+\dfrac{2}{x+1}:\dfrac{2x^2+2x-3x-3-2x^2+2x-x+1}{\left(x-1\right)\left(x+1\right)}\)

\(=\dfrac{\left(x-2\right)\left(x+2\right)}{x+1}+\dfrac{2}{x+1}\cdot\dfrac{\left(x-1\right)\left(x+1\right)}{-2}\)

\(=\dfrac{\left(x-2\right)\left(x+2\right)}{x+1}+\dfrac{-x+1}{1}\)

\(=\dfrac{x^2-4-\left(x-1\right)\left(x+1\right)}{x+1}\)

\(=\dfrac{x^2-4-x^2+1}{x+1}\)

\(=-\dfrac{3}{x+1}\)

a: Ta có: \(K=\left(\dfrac{2+x}{2-x}+\dfrac{x}{2+x}-\dfrac{4x^2+2x+4}{x^2-4}\right):\left(\dfrac{x^2+9}{x^2-2x}-\dfrac{2x}{x-2}\right)\)

\(=\dfrac{-x^2-4x-4+x^2-2x-4x^2-2x-4}{\left(x-2\right)\left(x+2\right)}:\dfrac{x^2+9-2x^2}{x\left(x-2\right)}\)

\(=\dfrac{-4x^2-8x-8}{\left(x-2\right)\left(x+2\right)}\cdot\dfrac{x\left(x-2\right)}{-x^2+9}\)

\(=\dfrac{-4\left(x^2+2x+1\right)}{x+2}\cdot\dfrac{x}{-\left(x-3\right)\left(x+3\right)}\)

\(=\dfrac{-4x\left(x+1\right)^2}{-\left(x-3\right)\left(x+3\right)\left(x+2\right)}\)

a) \(D=\left(\dfrac{2}{x+2}-\dfrac{4}{x^2+4x+4}\right):\left(\dfrac{2}{x^2-4}+\dfrac{1}{2-x}\right)\)\(=\left(\dfrac{2}{x+2}-\dfrac{4}{\left(x+2\right)^2}\right):\left(\dfrac{2}{\left(x-2\right)\left(x+2\right)}-\dfrac{1}{x-2}\right)\)

\(=\left(\dfrac{2\left(x+2\right)}{\left(x+2\right)^2}-\dfrac{4}{\left(x+2\right)^2}\right):\left(\dfrac{2}{\left(x-2\right)\left(x+2\right)}-\dfrac{x+2}{\left(x-2\right)\left(x+2\right)}\right)\)

\(=\dfrac{2\left(x+2\right)-4}{\left(x+2\right)^2}:\dfrac{2-x-2}{\left(x-2\right)\left(x+2\right)}\)

\(=\dfrac{2x+4-4}{\left(x+2\right)^2}:\dfrac{-x}{\left(x-2\right)\left(x+2\right)}\)

\(=\dfrac{2x}{\left(x+2\right)^2}.\dfrac{\left(x-2\right)\left(x+2\right)}{-x}\)

\(=\dfrac{-2.\left(x-2\right)}{x+2}\)

\(x^2-5x+6=0\\ \Rightarrow\left(x^2-2x\right)-\left(3x-6\right)=0\\ \Rightarrow\left(x-2\right)\left(x-3\right)=0\\ \Rightarrow\left[{}\begin{matrix}x-2=0\\x-3=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=2\\x=3\end{matrix}\right.\)

\(P=\dfrac{-2.\left(x-2\right)}{x+2}\)

Thay \(x=2\), ta có:

\(P=\dfrac{-2.\left(2-2\right)}{2+2}\)

    \(=0\)

Thay \(x=3\), ta có:

\(P=\dfrac{-2.\left(3-2\right)}{3+2}\)

    \(=-\dfrac{2}{5}\)

Là D kìa, lần sau ghi các câu nhỏ để dễ thấy, với cả còn câu c kìa.