ĐKXĐ: \(x\ne-\dfrac{5}{6}\)

a) Để A>0 thì \(\left[{}\begin{matrix}7x-8>0\\6x+5< 0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}7x>8\\6x< -5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x>\dfrac{8}{7}\\x< -\dfrac{5}{6}\end{matrix}\right.\)

b) Để A<0 thì \(\left\{{}\begin{matrix}6x+5>0\\7x-8< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>-\dfrac{5}{6}\\x< \dfrac{8}{7}\end{matrix}\right.\Leftrightarrow-\dfrac{5}{6}< x< \dfrac{8}{7}\)

c) Để A=0 thì \(\dfrac{7x-8}{6x+5}=0\)

\(\Leftrightarrow7x-8=0\)

\(\Leftrightarrow x=\dfrac{8}{7}\)

Ok, mk sẽ làm rõ ra cho bạn !

Bài 1: 25-(45-x)=13

                 45-x =25-13

                 45-x =12

                      x =45-12

                      x =33.

Bài 2: 10+(2x-4)=16

                  2x-4 =16-10

                  2x-4 =6

                  2x    =6+4

                  2x    =10

                   x     =10:2

                  x      =5

Bài 3: 24+3(5-x)=27

                 3(5-x)=27-24

                3(5-x)=3

                   5-x =3:3

                  5-x =1

                     x =5-1

                     x =4

Bài 1

\(25-\left(45-x\right)=13\)

\(45-x=25-13\)

\(45-x=12\)

\(x=45-12\)

\(x=33\)

Bài 2

\(10+\left(2x-4\right)=16\)

\(2x-4=16-10\)

\(2x-4=6\)

\(2x=10\)

\(x=10:2\)

\(x=5\)

Bài 3

\(24+3\left(5-x\right)=27\)

\(27\left(5-x\right)=27\)

\(5-x=27:27\)

\(5-x=1\)

\(x=5-1\)

\(x=4\)

Chi tiết lắm rồ đóa !!!

\(\frac{6}{x}+\frac{1}{2}=2\)

\(\Rightarrow\frac{6}{x}=2-\frac{1}{2}\)

\(\Rightarrow\frac{6}{x}=\frac{3}{2}\Rightarrow6\times2=3\times x\Rightarrow12=3\times x\)

\(\Rightarrow x=12\div3=4\)

cách làm lớp 6:

\(\frac{6}{x}=2-\frac{1}{2}\)

\(\frac{6}{x}=\frac{2}{1}-\frac{1}{2}\)

\(\frac{6}{x}=\frac{3}{2}\)

6.2=3.x

12=3.x

=>3.x=12

x=12:3

x=4

\(\frac{6}{x}+\frac{1}{2}=2 \)
\(\frac{6}{x}=2-\frac{1}{2}\)
\(\frac{6}{x}=\frac{4}{2}-\frac{1}{2}\)
\(\frac{6}{x}=\frac{3}{2}\)
\(\Leftrightarrow3.x=6.2\)
\(\Leftrightarrow3x=12\)
\(\Leftrightarrow x=12:3\)
\(\Leftrightarrow x=4\)
Vậy x cần tìm là 4

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

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

a)(3x+2):8=4

3x+2=4.8

3x+2=32

3x=32-2

3x=30

x=30:3

x=10

b)x+2x+3x+4x=100

x(1+2+3+4)=100

x.10=100

x=100:10

x=10

b) x + 2x + 3x + 4x = 100

x( 1 + 2 + 3 + 4 ) = 100

x . 10 = 100

x = 100 : 10

x = 10

Bài 1: 

1 - 2  + 3 - 4 + .... + 2009 - 2010

= (1 - 2) + (3 - 4) + ... + (2009 - 2010)

= -1 .  1005

= -1005

Bài 2:

a) (15 - x) - (-x + 12) = 7 - (-5 + x)

=> 15 - x + x - 12 = 7 + 5 - x

=> -x + x + x = 7 + 5 - 15 + 12

=> x = 9

b) (x - 5)⁴ = (x - 5)⁶

=> x - 5 = 1 hoặc x - 5 = 0

=> x = 6 hoặc x = 5

c) (x + 1) + (x + 3) + ... + (x + 99) = 0

=> (x . 50) + (1 + 3 + ... + 99) = 0

=> (x . 50) + 2500 = 0

=> x . 50 = -2500

=> x = -50

Ta có : 1 - 2 + 3 - 4 + ..... + 2009 - 2010 

= (1 - 2) + (3 - 4) + ..... + (2009 - 2010)

= -1 + (-1) + ..... + (-1)

= -1.1005

= -1005

(8x−3)(3x+2)−(4x+7)(x+4)=(2x+1)(5x−1)(8x−3)(3x+2)−(4x+7)(x+4)=(2x+1)(5x−1)

 20x2−16x−34=10x2+3x−120x2−16x−34=10x2+3x−1

 10x2−19x−33=010x2−19x−33=0

 (10x+11)(x−3)=0

chỉ bt lm con b thoy

..army,,,,,,,,,,

a) \(\left(2x+3\right)\left(x-4\right)+\left(x-5\right)\left(x-2\right)=\left(3x-5\right)\left(x-4\right)\)

\(\Leftrightarrow3x^2-12x-2=3x^2-17x+20\)

\(\Leftrightarrow3x^2-12x=3x^2-17x+20+2\)

\(\Leftrightarrow3x^2-12x=3x^2-17x+22\left(3x^2-17x\right)\)

\(\Leftrightarrow5x=22\)

\(\Rightarrow x=\frac{22}{5}\)

b) \(\left(8x-3\right)\left(3x+2\right)-\left(4x+7\right)\left(x+4\right)=\left(2x+1\right)\left(5x-1\right)\)

\(\Leftrightarrow20x^2-16x-34=10x^2+3x+1\)

\(\Leftrightarrow20x^2-16x-33=10x^2+3x\)

\(\Leftrightarrow20x^2-16x-33=10x^2+3x-3x\)

\(\Leftrightarrow20x^2-16x-33=10x^2\)

\(\Leftrightarrow20x^2-16x-33=10x^2-10x^2\)

\(\Leftrightarrow20x^2-16x-33=0\)

\(\Rightarrow\orbr{\begin{cases}x=3\\x=-\frac{11}{10}\end{cases}}\)

a, ( 2x + 3 )(x - 4) + ( x - 5 )( x - 2) =( 3x - 5 ) ( x - 4 )
<-> 2x² - 8x + 3x - 12 + x² - 2x - 5x + 10 = 3x² - 12x - 5x + 20
<-> 3x² - 10x - 2 = 3x² - 15x + 20
<-> 3x² - 3x² - 10x + 15x = 20 + 2
<-> 5x = 22
<-> x = 22/5