126 + (–20) + 2004 + (–106)

= (126 – 20) + 2004 +(–106)

= 106 + 2004 + (–106)

= 106 + (–106) + 2004 (tính chất giao hoán).

= 0 + 2004

= 2004.

a) 126+(−20)+2004+(−106)126+(−20)+2004+(−106)

=2004+126+[(−20)+(−106)]=2004+126+[(−20)+(−106)]

=2004+126+[−(20+106)]=2004+126+[−(20+106)]

=2004+126+(−126)=2004+126+(−126)

=2004+[126+(−126)]=2004+0=2004=2004+[126+(−126)]=2004+0=2004.

b) (−199)+(−200)+(−201)=−(199+200+201)(−199)+(−200)+(−201)=−(199+200+201)

=−(199+201+200)=−[(199+201)+200]=−(199+201+200)=−[(199+201)+200]

=−(400+200)=−600=−(400+200)=−600.

a/ (- 2010) - (119 - 2010)

= (- 2010) - 119 + 2010

= - 119

b/ 217 + [43 + (- 217) + (- 23)]

= 217 + [43 + (-217) - 23]

= 217 + (-217) + 20

= 20

Bài 2: Tính bằng cách hợp lý nhất:

 a) (-2010) – (119 -2010)

= -2010 - 119 + 2010

= 2010 - 2010 - 119

=     0 - 119

= -119

b) 217 +[ 43 + (-217) +(-23)]

= 217 +  43 - 217 - 23

= ( 217 - 217 ) + ( 43 - 23 )

=        0            + 20

= 20

c) (18+29)+(158 -18 -29)       

= 18 + 29 + 158 - 18 - 29

= ( 18 - 18 ) + ( 29 - 29 ) + 158

=       0        +       0         + 158

= 158

d) 126 +(-20) +2004+(-106)

= 126 - 20 + 2004 - 106

= [( 126 - 20 ) - 106 ] + 2004

= [ 106 - 106 ] + 2004

=      0 + 2004

= 2004

e) (-199) +(-200) +(-201)

= -199 - 200 - 201

= -199 - 201 - 200

= - 400 - 200

= -600

f) 99 + (-100) +101   

= 99 - 100 + 101

= 99 + 101 -100

= 200 - 100

= 100

= 2004

2004

2004

126+106+(-20)+2004

=[126+(-20)]+[106+2004]

=106+2110

=2216

\(126+\left(-20\right)+2004+\left(-106\right)\)

\(=126-20+2004-106\)

\(=106+2004-106\)

\(=2110-106\)

\(=2004\)

a) 126 + (-20) + 2004 + (-106) = 106 + 2004 + (-106) = 106 + (-106) + 2004 = 0 + 2004 = 2004

126 + (-20) + 2004 + (-106)

= 126 + 2004 + (-20) + (-106)

= 2130 + (-20) + (-106)

= 2110 + (-106)

= 2004

= 0

= 2004

(-404)+1002+(-2000)+1998+(-596)

=[1002+1998+(-2000)]+[(-404)+(-596)]

= 0+0=0

126+(-20)+2004+(-106)

={126+[(-20)+(-106)]+2004

=0 + 2004 =2004

a: \(\left(2345+45\right)-2345\)

\(=2345+45-2345\)

\(=45+\left(2345-2345\right)\)

=45+0

=45

b: \(\left(-2010\right)-\left(119-2010\right)\)

\(=-2010-119+2010\)

\(=\left(-2010+2010\right)-119\)

=0-119

=-119

c: \(\left(18+29\right)+\left(158-18-29\right)\)

\(=18+29+158-18-29\)

\(=158+\left(18-18\right)+\left(29-29\right)\)

=158+0+0

=158

d: \(126+\left(-20\right)+2004+\left(-106\right)\)

\(=126-20+2004-106\)

\(=\left(126-20-106\right)+2004\)

=0+2004

=2004

e: \(\left(-199\right)+\left(-200\right)+\left(201\right)\)

\(=-199-200+201\)

\(=-199+\left(201-200\right)\)

=-199+1

=-198

f: \(99+\left(-100\right)+101\)

\(=\left(99+101\right)-100\)

=200-100

=100

g: \(217+\left[43+\left(-217\right)+\left(-23\right)\right]\)

\(=217+43-217-23\)

\(=\left(217-217\right)+\left(43-23\right)\)

=0+20

=20