x-681=1511+1206

x-681=2717

x=3398

x - 681 = 1511 + 1206

x - 681 = 2717

x          = 2717 + 681

x          = 3398

a ) x − 1 2 = 7 13 . 13 28 ; x − 1 2 = 1 4 b ) x 15 = − 3 11 . 77 36 ; x 15 = − 7 12 ; x = 15. − 7 12 c ) x + 7 7 = 9 18 . 9 27 ; x + 1 = 1 6 d ) x : 15 11 = − 3 12 .8 ; x : 15 11 = − 2 ; x = ( − 2 ) . 15 11

1206 : x + 342 : x = 6                                  24 x X - 15 x X = 1980

=> ( 1206 + 342 ) : x = 6                              => ( 24 - 15 ) x X = 1980

=> 1548 : x = 6                                           => 9 x X = 1980

=> x = 1548 : 6                                           => x = 1980 : 9

=> x = 258                                                  => x = 220

*** ủng hộ mik nha bạn !!!

a)1206/x+342/x=6

1206*1/x+342*1/x=6

(1206+342)*1/x=6

1548*1/x=6

1/x=1548/6

1/x=258

x=1/258

b)24*x-15*x=1980

(24-15)*x=1980

9*x=1980

x=1980/9

x=220

5: (x-1)(x-5)=(x-1)(x-2)

=>(x-1)(x-5)-(x-1)(x-2)=0

=>(x-1)(x-5-x+2)=0

=>-3(x-1)=0

=>x-1=0

=>x=1

6: \(6\left(x-3\right)\left(x-4\right)-6x\left(x-2\right)=4\)

=>\(6\left(x^2-7x+12\right)-6x^2+12x=4\)

=>\(6x^2-42x+72-6x^2+12x=4\)

=>-30x=4-72=-68

=>\(x=\frac{68}{30}=\frac{34}{15}\)

7: -(x+3)(x-4)+(x+1)(x-1)=10

=>\(-\left(x^2-x-12\right)+x^2-1=10\)

=>\(-x^2+x+12+x^2-1=10\)

=>x+11=10

=>x=-1

8: (2x-1)(x-2)-(2x-7)(x+3)=3

=>\(2x^2-4x-x+2-\left(2x^2+6x-7x-21\right)=3\)

=>\(2x^2-5x+2-\left(2x^2-x-21\right)=3\)

=>\(2x^2-5x+2-2x^2+x+21=3\)

=>-4x+23=3

=>-4x=-20

=>x=5

9: \(\left(x-5\right)\left(4-x\right)-\left(x-1\right)\left(x+3\right)=-2x^2\)

=>\(-\left(x^2-9x+20\right)-\left(x^2+2x-3\right)=-2x^2\)

=>\(-x^2+9x-20-x^2-2x+3=-2x^2\)

=>7x-17=0

=>7x=17

=>x=17/7

10: (4x+1)(x-3)-(x-7)(4x-1)=15

=>\(4x^2-12x+x-3-\left(4x^2-x-28x+7\right)=15\)

=>\(4x^2-11x-3-4x^2+29x-7=15\)

=>18x-10=15

=>18x=25

=>x=25/18

11: \(\left(x+1\right)\left(x^2-x+1\right)-x\left(x^2-3\right)=4\)

=>\(x^3+1-x^3+3x=4\)

=>3x=4-1=3

=>x=1

12: \(\left(x-3\right)\left(x^2+3x+9\right)+x\left(5-x^2\right)=6x\)

=>\(x^3-27+5x-x^3=6x\)

=>6x=5x-27

=>x=-27

13: (3x-5)(x+1)-(3x-1)(x+1)=x-4

=>(x+1)(3x-5-3x+1)=x-4

=>-4(x+1)=x-4

=>-4x-4=x-4

=>-4x-x=0

=>-5x=0

=>x=0

14; 5(x-3)(x-7)-(5x+1)(x-2)=8

=>\(5\left(x^2-10x+21\right)-\left(5x^2-10x+x-2\right)=8\)

=>\(5x^2-50x+105-5x^2+9x+2=8\)

=>-41x=8-2-105=6-105=-99

=>x=99/41

kn Trần tuân

sao bn hay hỏi về cái này nhỉ

a) \(\frac{3}{7}x=\frac{8}{13}y=\frac{6}{19}z\) và 2x-y-z =-6

=)\(\frac{x}{\frac{7}{3}}=\frac{y}{\frac{13}{8}}=\frac{z}{\frac{19}{6}}=\frac{2x}{\frac{14}{3}}=\frac{y}{\frac{13}{8}}=\frac{z}{\frac{19}{6}}\)

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

\(\frac{2x}{\frac{14}{3}}=\frac{y}{\frac{13}{8}}=\frac{z}{\frac{19}{6}}=\frac{2x-y-z}{\frac{14}{3}-\frac{13}{8}-\frac{19}{6}}=\frac{-6}{\frac{-3}{24}}=48\)

\(\Rightarrow\frac{x}{\frac{7}{3}}=48\Rightarrow x=48\times\frac{7}{3}=112\)

\(\Rightarrow\frac{y}{\frac{13}{8}}=48\Rightarrow y=48\times\frac{13}{8}=78\)

\(\Rightarrow\frac{z}{\frac{19}{6}}=48\Rightarrow z=48\times\frac{19}{6}=152\)

Vậy x=112;y=78;z=152

1206 x 1317 = 1588302.

=1588302