mik nhầm nha, phải là:

138x=966

=> x=7

Ta có : 

\(\frac{3x-1}{40-5x}=\frac{25-3x}{5x-34}\)

\(=>\left(3x-1\right)\left(5x-34\right)=\left(40-5x\right)\left(25-3x\right)\)

\(=>15x^2-102x-5x+34=1000-120x-125x+15x^2\)

\(=>15x^2-107x+34=1000-245x+15x^2\)

\(=>34-107x=1000-245x\)

\(=>1000-245x+107x=34\)

\(=>1000-138x=34\)

\(=>138x=1000-34=966\)

\(=>x=\frac{966}{138}=7\)

theo đề bài ta có: \(\left(3x-1\right)\left(5x-34\right)=\left(40-5x\right)\left(25-3x\right)\)

=> \(15x^2-107x+34=1000-245x+15x^2\)

<=> 138*x^2=966

<=>x^2=7

<=>x=\(\pm\sqrt{7}\)

=>(2x+3).(10x+2)=(5x+2).(4x+5)

=>(2x.10x)+(2x.2)+(3.10x)+(3.2)=(5x.4x)+(5x.5)+(2.4x)+(2.5)

=>20x²+4x+30x+6=20x²+25x+8x+10

=>20x²-20x²+4x-8x+30x-25x=10-6

=>0+4x-8x+30x-25x=4

=>-4x+30x-25x=4

=>26x-25x=4

=>x=4

B)=>(3x-1).(5x-34)=(40-5x).(25-3x)

=>15x²-102x-5x+34=1000-120x-125x+15x²

=>15x²-107x+34=1000-245x+15x²

=>15x²-15x²-107x+245x=1000-34

=>0-107x+245x=966

=>138x=966

=>x=7

A,=>(2x+3).(10x+2)=(5x+2).(4x+5)

=>(2x.10x)+(2x.2)+(3.10x)+(3.2)=(5x.4x)+(5x.5)+(2.4x)+(2.5)

=>20x2+4x+30x+6=20x2+25x+8x+10

=>20x2-20x2+4x-8x+30x-25x=10-6

=>0+4x-8x+30x-25x=4

=>-4x+30x-25x=4

=>26x-25x=4

=>x=4

\(\frac{3x-1}{40-5x}=\frac{25-3x}{5x-34}\)

=> (3x-1).(5x-34)=(40-5x).(25-3x)

=> 3x.(5x-34)-(5x-34)= 40.(25-3x)-5x.(25-3x)

=> 15x²-102x-5x+34= 1000-120x-125x+15x²

=> 15x²- 107x+34 = 1000-245x+15x²

=> 107x+34 =1000-245x

=> 138x=966

=> x=7

3x + 5x= 40

=> 8x = 40

=> x = 5

3x + 5x=40 

=> 8x=40

=> x=5

3x + 5x= 40

8x         = 40

x           = 40:8

x           = 5

\(\frac{40-5x}{24+3x}=\frac{80-5x}{48+3x}=\frac{80-5x-\left(40-5x\right)}{48+3x-\left(24+3x\right)}=\frac{40}{24}=\frac{5}{3}\)

3( 40-5x) = 5( 24+3x)  

120 - 15x = 120 + 15x

30x =0 => x =0