10x-138=262

10x      =262+138

10x      =400

  x        = 400:10

 x       = 40

(10x + 120) - 138 = 262

10x+120=262+138

10x+120=400

10x=400-120

10x=280

x=280:10

x=28

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\(\text{205 x 352 - 6930 : 165 = 72160 - 42 = 72118 }\)                     \(\text{8694 : 138 : 21 = 63 : 21 = 3}\)

Hok Tốt !

# mui #

\(2\left(x-5\right)+10=20\)

\(\Leftrightarrow2\left(x-5\right)=10\)

\(\Leftrightarrow x-5=5\)

\(\Leftrightarrow x=10\)

\(\left(3x+1\right)-17=5\)

\(\Leftrightarrow3x+1=22\)

\(\Leftrightarrow3x=21\)

\(\Leftrightarrow x=7\)

\(\left(10x+120\right)-138=262\)

\(\Leftrightarrow10x+120=400\)

\(\Leftrightarrow10x=280\)

\(\Leftrightarrow x=28\)

\(4\left(x+1\right)-12=8\)

\(\Leftrightarrow4\left(x+1\right)=20\)

\(\Leftrightarrow x+1=5\)

\(\Leftrightarrow x=4\)

\(2x+2\frac{1}{3}=\frac{1}{2}:\frac{3}{2}\)

\(\Leftrightarrow2x+\frac{7}{3}=\frac{1}{3}\)

\(\Leftrightarrow2x=-2\)

\(\Leftrightarrow x=-1\)

\(2\left(x-5\right)+10=20\)

\(2x-10+10=20\)

\(2x=20\)

\(x=10\)

\(\left(3x+1\right)-17=5\)

\(3x+1-17=5\)

\(3x-16=5\)

\(3x=21\)

\(x=\frac{21}{3}=7\)

\(\left(10x+120\right)-138=262\)

\(10x+120-138=262\)

\(10x-18=262\)

\(10x=280\)

\(x=28\)

\(4\left(x+1\right)-12=8\)

\(4x+4-12=8\)

\(4x-8=8\)

\(4x=16\)

\(x=4\)

2.(x-5)+10 = 20

2.(x-5) = 20 - 10

2.(x-5) = 10

x-5 = 10 : 2

x-5 = 5

x = 5 + 5

x = 10

(3x+1)-17 = 5

3x+1 = 5 + 17

3x+1 = 22

3x = 22 - 1

3x = 21

x = 21 : 3

x = 7

(10x+120)-138 = 262

10x+120 = 262 + 138

10x+120 = 400

10x = 400-120

10x = 280

x = 280 : 10

x = 28

4.(x+1)-12 = 8

4.(x+1) = 8 + 12

4.(x+1) = 20

x+1 = 20 : 4

x+1 = 5

x = 5 - 1

x = 4

\(2x+2\frac{1}{3}=\frac{1}{2}:\frac{3}{2}\)

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

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

\(2x=-2\)

x = (-2) : 2

x = -1

đặt B=35 + 335 + 3335 + ..........(33.....335)
B-2.99=33+333+3333+...+(333....333)

(số cuối có 99 chữ số 3)

3.(B-2.99)=99+999+9999+....+(999...999...

(số cuối có 99 chữ số 9)

3(B-198)+99=100+1000+10000+....+(100..... (có 99 số 0)

3(B-198)+99=10^2+10^3+...+10^99
=(10^100-10^2)/9 (áp dụng công thức tính CSN)

=>3(B-198)+99=(10^100-10^2)/9

3705-(335-480)+(335-375)

=3705-335+480+335-375

=3705+(-335+335)+(480-375)

=3705+0+105

=3810

kết quả cộng lại = 3810