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Bài 1:
a.
$-12-(-46)=-12+46=46-12=34$
b.
$-(-8)-54=8-54=-(54-8)=-46$
c.
$-15-(-72)=-15+72=72-15=57$
Bài 2:
a. $(156-812)-(156-12)=156-812-156+12$
$=(156-156)-(812-12)=0-800=-800$
b.
$-(-72+83)-(72+17)=72-83-72-17=(72-72)-(83+17)$
$=0-100=-100$
c.
$-(-23-78)+(77-178)=23+78+77-178$
$=(23+77)-(178-78)=100-100=0$
d.
$(-213-156)-(-213+44)=-213-156+213-44=(-213+213)-(156+44)$
$=0-200=-200$
[(6x - 72) : 2 - 84]. 28 = 5628
=> (6x - 72) : 2 - 84 = 5628 : 28 = 201
=> (6x - 72) : 2 = 201 + 84 = 285
=> 6x - 72 = 285 . 2 = 570
=> 6x = 570 + 72 = 642
=> x = 642 : 6
=> x = 107
\(a,\left(2600+6400\right)-3\times x=1200\)
\(9000-3\times x=1200\)
\(3\times x=9000-1200\)
\(3\times x=7800\)
\(x=7800:3\)
\(x=2600\)
\(b,\left[\left(6\times x-72\right):2-84\right]\times28=5628\)
\(\left(6\times x-72\right):2-84=5628:28\)
\(\left(6\times x-72\right):2-84=201\)
\(\left(6\times x-72\right):2=201+84\)
\(\left(6\times x-72\right):2=285\)
\(6\times x-72=285\times2\)
\(6\times x-72=570\)
\(6\times x=570+72\)
\(6\times x=642\)
\(x=107\)
\(c,2x-138=2^3:3^2\)
\(2x-138=\frac{8}{9}\)
\(2x=\frac{8}{9}+138\)
\(2x=\frac{1250}{9}\)
\(x=\frac{1250}{9}:2\)
\(x=\frac{625}{9}\)
\(d,42x=39\times42-37\times42\)
\(42x=42\times\left(39-37\right)\)
\(42x=42\times2\)
\(42x=84\)
\(x=2\)
1) 2155-(174+2155)+(-68+174-7)-1911-(1234-1911)
=2155-174-2155+(-68)+174-7-1911-1234+1911
=(2155-2155)+(174-174)+(1911-1911)-(68+7+1234)
= 0 + 0 + 0 - 1309
= -1309
1) -1911 -( 1234 -1911)
= -1911 - 1234 + 1911 = -1234
2) 156.72+ 28. 156
= 156.(72+28)
= 156. 100
= 15600
3)32. (-39) + 16.(-22)
= 16.2.(-39) + 16.(-22)
= 16. (-78) + 16.(-22)
= 16.[(-78) + (-22)]
= 16. (-100)
= -1600
4) -1954 - (567 - 1954)
= -1954 - 567 + 1954
= -567
5)184. 33 + 67. 184
= 184.(33+ 67)
= 184. 100
= 18400
6) 44. (-36) + 22. (-28)
= 22.2.(-36) + 22.(-28)
= 22.(-72) + 22.(-28)
= 22. [(-72)+ (-28)]
= 22. (-100)
= -2200
1) -1911 - (1234 - 1911)
= -1911 - 1234 + 1911
= (-1911 + 1911 ) + 1234
= 0 + 1234
= 1234
2) 156 . 72 + 28 . 156
= 156 . ( 72 + 28 )
= 156 . 100
= 15600
3) 32 . (-39) + 16 . (-22)
= [ 32 . (-39) ] + [ 16 . (-22) ]
= -1248 + (-352)
= - 1600
4) -1954 - (567 - 1954)
= -1954 - 567 + 1954
= (-1954 + 1954) + 567
= 0 + 567
= 567
5) 184 . 33 + 67 . 184
= 184 . (33 + 67)
= 184 . 100
= 18400
6) 44 . ( -36) + 22 . (-28)
= [ 44 . (-36) ] + [ 22 . (-28) ]
= -1584 + (-616)
= -2200
a: -x+5/9=-1/3
nên x=5/9+1/3=5/9+3/9=8/9
b: \(\Leftrightarrow\dfrac{1}{5}+\dfrac{1}{10}+\dfrac{11}{15}< x< \dfrac{1}{2}+\dfrac{13}{12}+\dfrac{1}{3}\)
=>31/30<x<23/12
mà x là số nguyên
nên \(x\in\varnothing\)
c: x+5/3=1/81
nên x=1/81-135/81=-134/81
\(\Leftrightarrow3\cdot4^{2x+1}=36+156=192\)
=>2x+1=3
hay x=1
\(3.4^{2x+1}-156=72:2\)
\(3.4^{2x+1}-156=36\)
\(4^{2x+1}-156=36:3\)
\(4^{2x+1}-156=12\)
\(4^{2x+1}=12+156\)
\(4^{2x+1}=168\)
\(2x+1=168:4\)
\(2x+1=42\)
\(x+1=42:2\)
\(x+1=21\)
\(x=21-1\)
\(x=20\)