+) 5x - 16 = 40 + x

<=> 5x - x = 16 + 40

<=> 4x = 56

<=> x = 56 : 4

<=> x= 14

+) 3x - 6 = 5x + 2

<=> 3x - 5x = 6 + 2

<=> -2x = 8

<=> x =- 4

+) x + 15 = 20 - 4x

<=> x + 4x = 20 - 15

<=> 5x = 5

<=> x= 1 

+) -12 + x = 5x -20

<=> x - 5x = 12 - 20

<=> -4x = -8

<=> x= 2

T^T , T sai chỗ nào vậy

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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=\(\pm\sqrt{7}\)

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

=> (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

áp dụng tính chất của dãy tỉ số bằng nhau ta có;

\(\frac{3x-1}{40-5x}=\frac{25-3x}{5x-34}=\frac{3x-1+25-3x}{40-5x+5x-34}=\frac{24}{6}=4\)

suy ra:

\(\frac{3x-1}{40x-5}=4\Rightarrow3x-1=4.\left(40-5x\right)\)

3x-1=160-20x

3x+20x=160+1

23x=161

x=161:23

x=7

vậy x=7

a) \(\frac{2x+3}{5x+2}=\frac{4x+5}{10x+2}\)

\(\Leftrightarrow\)\(\left(2x+3\right)\left(10x+2\right)=\left(5x+2\right)\left(4x+5\right)\)

\(\Leftrightarrow20x^2+4x+30x+6=20x^2+25x+8x+10\)

\(\Leftrightarrow20x^2-20x^2+4x+30x-25x-8x=10-6\)

\(\Leftrightarrow x=4\)

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

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

\(\Leftrightarrow15x^2-102x-5x+34=1000-120x-125x+15x^2\)

\(\Leftrightarrow15x^2-15x^2-102x-5x+120x+125x=1000-34\)

\(\Leftrightarrow138x=966\)

\(\Leftrightarrow x=7\)

a ) \(\frac{2x+3}{5x+2}=\frac{4x+5}{10x+2}\)

\(\left(2x+3\right).\left(10x+2\right)=\left(5x+2\right)\left(4x+5\right)\)

\(20x^2+4x+30x+6=20x^2+25x+8x+10\)

\(4x+30x-25x-8x=10-6\)

\(x=4\)

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

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

\(\Leftrightarrow15x^2-102x-5x+34=1000-120x-125x+15x^2\)

\(\Leftrightarrow-102x-5x-120x-125x=1000-34\)

\(\Leftrightarrow-352x=966\)

\(\Leftrightarrow x=-\frac{483}{176}\)

Áp dụng tính chất của dãy tỉ số bằng nhau ta có:

\(\frac{2x+3}{5x+2}=\frac{4x+5}{10x+2}=\frac{2.\left(2x+3\right)-\left(4x+5\right)}{2.\left(5x+2\right)-\left(10x+2\right)}=\frac{4x+6-4x-5}{10x+4-10x-2}=\frac{1}{2}\)

Suy ra:

\(\frac{2x+3}{5x+2}=\frac{1}{2}\Rightarrow2.\left(2x+3\right)=1.\left(5x+2\right)\Rightarrow4x+6=5x+2\)

\(\Rightarrow x=4\)

=>(3x+2)(5x+1)=(5x+7)(3x-1)

(3x)(5x+1)+2(5x+1)=(5x)(3x-1)+7(3x-1)

15x²+3x+10x+2=15x²-5x+21x-7

(15x²-15x²)+(3x+10x+5x-21x)=-7-2

0-3x=-9

-3x=-9

x=(-9)/(-3)

x=3

\(\frac{3x+2}{5x+7}\)=\(\frac{3x-1}{5x+1}\)

\(\Rightarrow\)\(\frac{3x+2}{3x-1}\)= \(\frac{5x+7}{5x+1}\)\(\Rightarrow\)1+\(\frac{3}{3x-1}\)=1+\(\frac{6}{5x+1}\)

\(\Rightarrow\)\(\frac{3}{3x-1}\)= \(\frac{6}{5x+1}\)\(\Rightarrow\)3.(5x+1) = 6.(3x-1)

\(\Rightarrow\)15x+3 = 18x -6

\(\Rightarrow\)3x = 6 +3

\(\Rightarrow\)x =3