31.(-18) + 31.(-81) - 31

= 31.(-18 - 81 - 1)

= 31.(-100) = -3100

-48 + 48.(-78) + 48.(-21) = 48.(-1 - 78 - 21) = 48. (-100) = -4800

-75.(8 - 65) - 65.(75 - 18) = -75.18 + 75.65 - 65.75 + 65.18 = 0

29.(19 - 13) - 19.(29 - 13) = 29.19 - 29.13 - 19.29 + 19.13 = 0

13.(23 + 22) - 3(17 + 28) = 13.25 - 3.45 = (10 + 3).25 - 3.45

= 10 . 25 + 3.25 - 3.45 = 10.25 - 3.(45 - 25)

= 250 - 3.20 = 250 - 60 = 190

(-25).21 . (-2)².(|3|). (-1)^{2n + 2} (n \(\in\)N*)

= (-25. 4) . (21.3).1

= -100. 63 = -6300

Các hỗn só và phân số = nhau là:5/3=1 12/18; 5 9/31=1 29/65; 55/14=5 13/44; 94/65=164/31;2 7/13=66/26

a)

(-12)(-13)+13(-22) = 12.13 - 13.22 = 13(12-22)=13.(-10)=-130

b) 15(-14) +15(-6) + (-20).25 = 15[(-14)+(-6)]+(-20).25=15.(-20)+(-20).25=(-20)(15+25)=-20.40=-800

c) -65.(87-17)-87(17-65) = 

a)(-12).(-13)+13.(-22)=12.13+13.(-22)=13.[12+(-22)]=13.(-10)=-130

b)15.(-14)+15.(-6)+(-20).25=15.[(-14)+(-6)]+(-20).25=15.(-20)+(-20).25=(-20).(15+25)=(-20).40=-800

c)-65.(87-17)-87.(17-65)=-65.87-(-65).17-87.17+87.65

=-65.87+65.17-87.17+87.65

=[(-65)+65].87+(65-87).17

=0.87+(-22).17

=0+(-374)=-374

a) 125-(-75)+32-(48+32) = 125 + 75 + 32 - 48 - 32 = 200 - 48 = 152

b) 47.347+347.(-47) = 347.( 14 - 47 ) = 347 . 0 = 0

c) x-10=-14

x = -14 +10

x = -4

d) 15 + x = 13

x = 13 - 15

x = -2

e) 25 . x = -75

x = -75/25

x = -3

g) 5x - 16 = -46

5x = -46 + 16

5x = - 30

x = -6

i) 3x - (-11) = -4

3x + 11 = -4

3x = -4 - 11

3x = -15

x = -5

hok tốt!!

\(-8.4+19=-32+19=-13\)

\(-11.3-28=-33-28=-61\)

\(4.\left(-15\right)-18=-60-18=-78\)

\(19-4.\left(-12\right)=19+48=67\)

\(-25.\left(-3\right)-54=75-54=21\)

\(-16-7.\left(-4\right)+24\div\left(-8\right)=-16+28-3=9\)

\(15\div\left(-3\right)+30-7.\left(-3\right)=-5+30+21=46\)

\(-48\div\left(-4\right)+15.\left(-5\right)=12-75=-63\)

\(-29+65\div\left(-5\right)+23=-29-13+23=-19\)

\(15\div\left(-5\right)-17-12.\left(-5\right)=-3-17+60=40\)

\(28.\left(-4\right)-17=-112-17=-129\)

\(-19-7.4=-19-28=-47\)

\(-14.\left(-2\right)-16=28-16=12\)

\(13.\left(-3\right)-65-4.\left(-6\right)=-39-65+24=-80\)

\(-24-8.\left(-6\right)+28=-24+48+28=52\)

Chúc bạn hok tốt!!! tỷ tỷ

( 12 + 68) + ( 13 + 67 ) + (14 + 66 ) + (15 + 65 ) ( 0.5 )

= 80 + 80 + 80 + 80 ( 0.5 )

= 80 x 4 = 320 ( 0.5 )

b. Tìm được số a : 16 : 2 = 8

1/4 của số a là : 8 : 4 = 2 

Đáp số: 2                      

a) \(A=\left(-13\right)+\left(-27\right)+\left(-65\right)\)

        \(=-105\)

b) \(B=\left(-9\right)+\left(-14\right)+27\)

         \(=4\)

A)x+12=12+6

x=18-12

x=6

b)x-21=33-21

x=12+21

x=33

c)14-x=14-2

x=16-14

x=2

d)x-48=65-28

x=37+48

x=85

e)65-x=48+17

x=65-65

x=0

a,x+12=12+6

  x+12=18

       x=18-12

       x=6

   b,   x-21=33-21

      x-21=12

         x=12+21

         x=33

c, 14-x=14-2

    14-x=12

        x=14-12

        x=2

d,x-48=65-28

  x-48=37

      x=37+48

      x=85

e,65-x=48+17

  65-x =65

      x=65-65

      x=0