x+2/2+x+ 2/6 +x+ 2/12 +...+x+  2/110 = 130/11

=> x +2/1.2 + x +2/2.3 + x +2/3.4 +...+ x +2/10.11 = 130/11

=> 10 x + 2/1.2+2/2.3+....+2/10.11 = 130/11

=> 10 x + 2. [ 1/1.2+1/2.3+...+1/10.11] = 130/11

=> 10 x + 2. [1-1/2+1/2-1/3+...+1/10-1/11] = 130/11

=> 10 x + 2 [1-1/11] = 130/11

=> 10 x + 2 x 10/11 = 130/11

=> 10 x +20/11 = 130/11

=> 10 x = 10 => x= 10 : 10=1

a) \(\dfrac{6}{13}:\left(\dfrac{1}{2}-x\right)=\dfrac{15}{39}\)

\(\dfrac{1}{2}-x=\dfrac{6}{13}:\dfrac{15}{39}\)

\(\dfrac{1}{2}-x=\dfrac{6}{5}\)

\(x=\dfrac{1}{2}-\dfrac{6}{5}\)

\(x=-\dfrac{7}{10}\)

b) \(3\times\left(\dfrac{x}{4}+\dfrac{x}{28}+\dfrac{x}{70}+\dfrac{x}{130}\right)=\dfrac{60}{13}\)

\(3\times x\times\left(\dfrac{1}{4}+\dfrac{1}{28}+\dfrac{1}{70}+\dfrac{1}{130}\right)=\dfrac{60}{13}\)

\(x\times\left(\dfrac{3}{1\times4}+\dfrac{3}{4\times7}+\dfrac{3}{7\times10}+\dfrac{3}{7\times13}\right)=\dfrac{60}{13}\)

\(x\times\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}\right)=\dfrac{60}{13}\)

\(x\times\left(1-\dfrac{1}{13}\right)=\dfrac{60}{13}\)

\(x\times\dfrac{12}{13}=\dfrac{60}{13}\)

\(x=\dfrac{60}{13}:\dfrac{12}{13}\)

\(x=5\)

198 - 42 : 6 . x + 16 = 130

=> 214 - 7.x = 130

=> 7.x = 214 - 130

=> 7.x = 84

=> x = 84 : 7

=> x = 12

(. là nhân)

#)Giải :

   198 - 42 : 6 x X + 16 = 130

   198 - 7 x X + 16       = 130 

   198 - 7 x X               = 130 - 16

   198 - 7 x X               = 114

           7 x X                = 198 - 114

           7 x X                = 84

                 X                = 84 : 7

                 X                = 12 

        #~Will~be~Pens~#

12 { [ 18 - ( 6 : x + 3 ) ] - 3 } = 130 - 10 = 120

18 - ( 6 : x + 3 ) - 3 = 120 : 12 = 10

18 - ( 6 : x + 3 ) = 10 + 3 = 13

6 : x + 3 = 18 - 13 = 5

6 : x = 5 - 3 = 2

x = 6 : 2 = 3

Vậy x = 3

130 - 12{[18 - (6 : x + 3)] - 3} = 10

12{[18 - (6 : x + 3)] - 3} = 130 - 10

12{[18 - (6 : x + 3)] - 3} = 120

18 - (6 : x + 3) - 3 = 120 : 12

15 - (6 : x + 3)  = 10

6 : x + 3 = 15 - 10

6 : x + 3 = 5

6 : x = 5 - 3

6 : x = 2

x = 6 : 2

x = 3

Vậy x = 3

a.

\(\left(3x-2^4\right)\times7^3=2\times7^4\)

\(3x-2^4=2\times7^4\div7^3\)

\(3x-16=2\times7\)

\(3x-16=14\)

\(3x=14+16\)

\(3x=30\)

\(x=\frac{30}{3}\)

\(x=10\)

b.

\(2130-\left(x+130\right)+72=-64\)

\(2130-\left(x+130\right)=-64-72\)

\(2130-\left(x+130\right)=-136\)

\(x+130=2130+136\)

\(x+130=2266\)

\(x=2266-130\)

\(x=2136\)

c.

\(15-\left(-x+18\right)=-24\)

\(\left(-x+18\right)=15+24\)

\(-x+18=39\)

\(-x=39-18\)

\(-x=21\)

\(x=-21\)

d.

\(10-\left|x+3\right|=-4-\left(-10\right)\)

\(\left|x+3\right|=10+4-10\)

\(\left|x+3\right|=4\)

\(x+3=\pm4\)

TH1:

\(x+3=4\)

\(x=4-3\)

\(x=1\)

TH2:

\(x+3=-4\)

\(x=-4-3\)

\(x=-7\)

Vậy x = 1 hoặc x = - 7.

bạn ơi câu b sao lại là 

(x=130)

a) \(x\in\left\{15;30;45\right\}\)

b) \(x\in\left\{12;24;36\right\}\)

c) \(x\in\left\{60;120\right\}\)

tự tính đi,bài dễ mà