a) X + 15 = 20

       X = 20 – 15

       X = 5

b) X – 18 = 16

       X = 16 + 18

       X = 34

c) 72 – x = 50

       X = 72 -50

       X =22

d) X x 7 = 42

       X= 42 : 7

       X = 6

e) X : 7 = 5

       X = 5 x 7

       X = 35

f) 49 : x = 7

       X = 49: 7

       X = 7

a) 84

b) -300

c) 1700

a) = 10 . ( 7.8 )

= 10 . 56 

= 560 

b) 

= 9.2.7.5

= ( 9.7 ) . ( 2.5 )

= 63 . 10 

= 630 

b) 7.x=42

x = 42 : 7 

x = 6

c) 180 : x = -12

x = 180 : ( -12 )

x = -15

b,84  c,-300  d,1700

a,=560  b,=630  

b)(-12).(-7)=84

c)15.(-20)=-300

D)34.50=1700

a)7.2.5.8

=2.5.7.8

=10.56

=560

b)9.2.(-7).(-5)

=2.(-5).9.(-7)

=(-10).(-63)

=630

b)7.x=42

      X=42:7

      X=6

c)180:x=-12

           x=180:(-12)

           x=-15

( 1/6  + 1/10  - 1/15) + x = 0

 1/5 + x           =0

        x           = -1/5

2)  => \(-\frac{5}{42}-x=-\frac{18}{28}\) => \(-x=\frac{5}{42}-\frac{18}{28}=\frac{10}{84}-\frac{54}{84}=-\frac{44}{84}\)

=>  \(x=\frac{44}{84}=\frac{11}{21}\)

3) => \(x=-\left(\frac{1}{6}+\frac{1}{10}-\frac{1}{15}\right)=-\left(\frac{10}{60}+\frac{6}{60}-\frac{4}{60}\right)=-\frac{12}{60}=-\frac{1}{5}\)

4) => \(\frac{x}{5}=\frac{2}{10}-\frac{1}{5}-\frac{7}{50}=\frac{1}{5}-\frac{1}{5}-\frac{7}{50}=-\frac{7}{50}\)

=> \(x=5.\frac{-7}{50}=-\frac{7}{10}\)

1)x-2/7=8/21

x=8/21+2/7=8/21+6/21=14/21

2)11/13-(5/42+x)=-18/28+11/16

=>-5/42-x=-18/28

x=-5/42-(-18/28)=-10/84+54/84=44/84=11/21

3)(1/6+1/10-1/15)+x=0

(5/30+3/30-2/15)+x=0

6/15+x=0

x=0-6/15

x=-6/15

4)-(-x)/5-2/10=-1/5-7/50

x/5-2/10=-10/50-7/50

x/5-2/10=-17/50

x/5=-17/50+2/10=-17/50+10/50

x/5=-7/50

=>10x/5=-7/50

10x=-7

x=-7/10

mk ko chắc đâu, tính nhẩm, có j tính lại nha

\(a.-14-x=-8\)

\(x=-6\)

\(b.11+x+20=32\)

\(31+x=32\)

\(x=1\)

\(c.5-\left(x-8\right)=63\)

\(x-8=-58\)

\(x=-50\)

a,\(\left(-14-x\right)+13=5\)

\(\Rightarrow-x+1=5\)

\(\Rightarrow-x=4\)

\(\Rightarrow x=-4\)

b,\(\left(11+x\right)-\left(-11-9\right)=32\)

\(\Rightarrow11+x+11+9=32\)

\(\Rightarrow x+31=32\)

\(\Rightarrow x=1\)

c,\(5-\left(x-8\right)+\left(-21\right)=42\)

\(\Rightarrow5-x+8-21=42\)

\(\Rightarrow-x-8=42\)

\(\Rightarrow x=-50\)

Điền kí hiệu toán học vào tất cả chỗ trong 3 số tự nhiên này : 10 10 10=6

10(81+19)+100+50(91+9)
=10.100+100+50.100
=1000+100+5000
=6100

=14.5.35+10.5.5.7+4.5.7

=70.35+50.35+4.35

=35.(70+50+4)

=35.124

=4340