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(-12) + (-18)

= -30

------------------

(-90) + 27 + (-10) + 73

= [(-90) + (-10) + (27 + 73)

= -100 + 100

= 0

---------------------------------

25 . (-5) . (-4)

= 25 . (-4) . (-5)

= -100 . (-5)

= 100 . 5

= 500

----------------------------------------

(-15) . 40 : 6

= [(-15) . 40] : 6 

= (-600) : 6

= -100

-----------------------------------

(-27) . 58 + (-27) . 42

= (-27) . (58 + 42)

= (-27) . 100

= -2700

Bài 2:

a. $=62-81-12+59-9=(62-12)+(59-9)-81$

$=50+50-81=100-81=19$

b. $=39+13-26-62-39=(39-39)+13-(26+62)$

$=0+13-88=-(88-13)=-75$

c. $=(32-42)+(36-34)+(40-38)=10+2+2=14$
d. $=92-55+8-45=(92+8)-(55+45)=100-100=0$

Bài 1:

a. $=(387-87)-224=300-224=76$

b. $=-(75+35)+379=-110+379=379-110=269$

c. $=(11+15)-(13+17)=25-30=-5$

d. $=(31-21)-(27-24)=10-3=7$

c) Ta có: \(\dfrac{3}{5}+\dfrac{-5}{20}+\dfrac{30}{75}+\dfrac{-7}{4}\)

\(=\dfrac{3}{5}+\dfrac{2}{5}+\dfrac{-1}{4}+\dfrac{-7}{4}\)

\(=1-2=-1\)

Giải:

a)-1/12+4/3=-1/12+16/12=15/12=5/4

b)(-4/14-3/15)-(1/5-20/35-(-1)).7

=-17/35-22/35.7

=-17/35-22/5

=-171/35

c)3/5+-5/20+30/75+-7/4

=3/5+-1/4+2/5+-7/4

=(3/5+2/5)+(-1/4+-7/4)

=1+-2

=-1

d)5/6.-12/14+7/13

=-5/7+7/13

=-16/91

e)2/-9-5/-36-1/4

=-1/12-1/4

=-1/3

f)2/23+-5/12+7/18+21/23+-7/12

=(2/23+21/23)+(-5/12+-7/12)+7/18

=1+-1+7/18

=7/18

`@` `\text {Ans}`

`\downarrow`

`1,`

`a)`

`-7/25 + (-8)/25`

`= (-7 - 8)/25`

`= -15/25`

`= -3/5`

`b)`

`6/13 + (-15)/39`

`= 18/39 + (-15)/39`

`= (18 - 15)/39`

`= 3/39`

`= 1/13`

`c)`

`5/7 + 4/(-14)`

`= 10/14 + (-4)/14`

`= (10 - 4)/14`

`= 6/14`

`= 3/7`

`d)`

`-8/18 + (-15)/27`

`= -4/9 + (-5)/9`

`= (-4-5)/9`

`= -9/9 = -1`

`2,`

`a)`

`3/5 + (-7)/4`

`= 12/20 + (-35)/20`

`= (12 - 35)/20`

`=-23/20`

`b)`

`(-2) + (-5)/8`

`= (-16)/8 + (-5)/8`

`= (-16 - 5)/8`

`= -21/8`

`c)`

`1/8 + (-5)/9`

`= 9/72 + (-40)/72`

`= (9-40)/72`

`= -31/72`

`d)`

`6/13 + (-14)/39`

`= 18/39 + (-14)/39`

`= (18 - 14)/39`

`= 4/39`

`e)`

`(-18)/24 + 15/21`

`= (-3)/4 + 5/7`

`= (-21)/28 + 20/28`

`= (-21 + 20)/28`

`= -1/28`

a) (-37) + 14 + 26 + 37

= [(-37) + 37] + (14 + 26)

= 0 + 40 = 40

b) (-24) + 6 + 10 + 24

= [(-24) + 24] + (10 + 6)

= 0 + 16 = 16

c) 15 + 23 + (-25) + (-23)

= [15 + (-25)] + [23 + (-23)]

= (-10) + 0 = -10

d) 60 + 33 + (-50) + (-33)

= [60 + (-50)] + [33 + (-33)]

= 10 + 0 = 10

e) (-16) + (-209) + (-14) + 209

= [(-16)  + (-14)] + [(-209) + 209]

= (-30) + 0 = -30

f) \(-3^2+\left(-54\right)\div\left[\left(-2\right)^8+7\right]\times\left(-2\right)^2\\ =\left(-9\right)+\left(-54\right)\div263\times4\\ =\left(-9\right)+\dfrac{-216}{263}=\dfrac{-2583}{263}\)

a. \(\left[\left(-37\right)+37\right]+\left(14+16\right)\) = 30 

B. \(\left[\left(-24\right)+24\right]+\left(10+6\right)\) = 16

C. \(\left[\left(-23\right)+23\right]+\left(15-23\right)\)= -8

d. \(\left[33-33\right]+\left(60-50\right)\) = 10

e. \(\left(209-209\right)+\left(-16-14\right)\)= -30

Bài 1: a,  73.74 + 73 + 73.65

           =  73.( 74 + 1 + 65)

           = 73. 140 = 10220

          b, (-45) +(-35) = - ( 35 + 45) = 80

          c, 299 - 6.[ (12 + 2): 5 - 3] 

             299 - 6.(2,8 - 3)

            299 - 6.(-0,2)

            299 + 1,2

           = 300,2

Bài 2: 

a, \(x-5\) = -15

   \(x\)        = -15 + 5

   \(x\)       = -10

b,  5\(x\) - 2.5 = 20.(-2)

    5\(x\)  - 10  = -40

    5\(x\)          = -40 + 10

     5\(x\)        = - 30 

       \(x\)        = - 6

c,   15 - \(x\)    = -3.4

     15 - \(x\)     = -12

             \(x\)   = 15 - ( -12)

             \(x\)   = 27