## Bài 1 : tính nhanh a. -28 + 32 – 45 – 32 + 28 + 45 – 8 b. 42 – 56 + 33 – ( 33 – 56 + 42 – 10 ) c. -5 – {- [ – ( -7 ) + ( -10 ) ]} – [ 5 – ( -12 ) –

Question

Bài 1 : tính nhanh
a. -28 + 32 – 45 – 32 + 28 + 45 – 8
b. 42 – 56 + 33 – ( 33 – 56 + 42 – 10 )
c. -5 – {- [ – ( -7 ) + ( -10 ) ]} – [ 5 – ( -12 ) – [ ( -3)- ( -9 ) – 4 -5 ]
d. | x + 2 | = 4

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17 phút 2021-11-26T06:32:42+00:00 2 Answers 0 views 0

1. a) -28+32-45-32+28+45-8

= [(-28)+28]+[32+(-32)]+[(-45)+45]+8

= 0+0+0+8

= 8

b) 42-56+33-(33-56+42-10)

= 42-56+33-33+56-42+10

= [42-42]+[(-56)+56]+(33-33)+10

= 0+0+0+10

= 10

c) -5-{-[-(-7)+ ( -10 ) ]} – [ 5 – ( -12 ) – [ ( -3)- ( -9 ) – 4 -5 ]

= -5+[7+(-10)]-[5+12-[(-3)+9-4-5]

= -5+(-3)-[5+12+3+9-4-5]

= -5+(-3)-20

= -28

d) |x+2|= 4

TH1: x+2= 4                                 TH2: x+2= -4

x= 4-2                                           x= -4-2

x= 2                                              x= -6

Vậy x∈{2; -6}

2. Đáp án:

a)-28 + 32 – 45 – 32 + 28 + 45 – 8

=(28-28)+(32-32)+(45-45)-8

=-8

b. 42 – 56 + 33 – ( 33 – 56 + 42 – 10 )

=42-56+33-33+56-42+10

=(42-42)+(56-56)+(33-33)+10

=10

c)-5-{-[-(-7)+ ( -10 ) ]} – [ 5 – ( -12 ) – [ ( -3)- ( -9 ) – 4 -5 ]`

=-5+(-3)-20

th1=4                                 th2-4

x

=2                                              =-6

Vậy