Bài 8: Quy tắc dấu ngoặc

Chọn C

x,y khác dấu

=>3(x+4)=105

=>x+4=35

=>x=31

128-3(x+4)=23

       3(x+4)=128-23

       3(x+4)=105

         (x+4)=105:3

         (x+4)=35

          x     = 35-4

          x     = 31

128 - 3(x+4) = 23

=>3(x+4) = 128-23

=>3(x+4) = 105

=> x+4 = 105:3

=>x+4 = 35

=> x = 35-4

=> x= 31

Vậy x = 31

\(12+23+\left(-20\right)+\left(-153\right)+8\)
\(=\left(12+8\right)+\left(-20\right)+\left[23+\left(-153\right)\right]\)
\(=20+\left(-20\right)-130\)
\(=0-130\)
\(=-130\)

-130

(x - 12)-15=(20-7)-18

x-12-15=20-7-18

x=20-7-18+12+15

x=22

<=> x - 27 = 13 - 18

x = 13 + 27 - 18 

=> x = 22

Bài 8:

1: \(=-5-9+\left(-18\right)+3=-14-15=-29\)

2: \(=-11+15-13-9-5\)

=4-13-9-5

=-9-9-5

=-18-5=-23

3: \(=-4+8-15-10=4-25=-21\)

4: \(=4+12-5+19=16-5+19=30\)

5: \(=-7+12-9+10=22-16=6\)

6: \(=-28+30-4=2-4=-2\)

7: \(=16+3-5-7+12=28+3-12=16+3=19\)

8: \(=13-\left(-1\right)+\left(-5\right)=8+1=9\)

Bài 1:

1: \(=8-9+10-14+12=9-2=7\)

2: \(=-14-13+9-5=-18-5=-23\)

3: \(=8-18-11=-10-11=-21\)

4: \(=-12+14-17-3=-32+14=-18\)

5: \(=17-15-2=0\)

6: \(=-4-4+8-4=-4\)

a: =210+46-210-26=20

b: =-8+5-8=-16+5=-11

c: =25(134-34)=2500

=10-12+(-9-1)=-12

10 - [12 - (-9 - 1)]

=10-10-(-12)

=0-12

=-12

10 - [12 - (-9 - 1)]

=10-10-(-12)

=0-12

=-12

a)

271 - [(-43) + 271 - (-17)]

=271-(-43+271+17)

=271+43-271-17

=271-271+43-17

=26

b)-144 - [29 - (+144) - (+144)]

=-144-(29-144-144)

=-144-29+144+144

=-144+144+144-29

=115

c)-[(-23 + 12) - (-23-7)] + (12 + 7)

=-(-23+12+23+7)+12+7

=+23-12-23-7+12+7

=23-23-12+12-7+7

=0

`(27+65)+(346-27-65)`

`=27+65+346-27-65`

`=(27-27)+(65-65)+346`

`=346`

(27 + 65) + (346 - 27 - 65)

= 27 + 65 + 346 - 27 - 65

= (27 - 27) + (65 - 65) + 346

= 0 + 0 + 346

= 346

`!`

`(27 + 65) + (346 - 27 - 65)`

`=27 + 65 + 346 - 27 - 65`

`=(28-27)+ (65-65) + 346`

`=0+0+346`

`=346`