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a, 2 3 x + 5 2 x = 2 5 2 + 2 3 - 33
8x+25x = 33
33x = 33
x = 1
b, 260 : x + 4 = 5 2 3 + 5 - 3 3 2 + 2 2
260:(x+4) = 5.13–3.13
x+4 = 260:26
x+4 = 10
x = 6
c, 720 : [ 41 - 2 x - 5 ] = 2 3 . 5
41–(2x–5) = 720:40
2x–5 = 41–18
2x = 28
x = 14
d, 3 2 - 2 x - 12 + 35 = 5 2 + 279 : 3 2
7(x–12)+35 = 56
7(x–12) = 21
x–12 = 3
x = 15
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Bài 2: Tính nhanh
a) 29 + 132 + 237 + 868 + 3
= 29+(132+858)+(237+3)
=29+990+240
=1259
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x - ( 17 - x ) = x + 3
<=> 2x - 17 = x + 3
<=> x = 20
Vậy x = 20
- ( x + 12 ) + 35 = - 47
<=> - x - 12 = - 47 -35
<=> x = 47 + 35 - 12
<=> x = 60
Vậy x = 60
15 - ( x + 32 ) = - 11
<=> 15 - x - 32 = - 11
<=> - x - 17 = - 11
<=> - x = - 11 + 17 = 6
<=> x = - 6
Vậy x = - 6
K chắc lắm
a)\(x-\left(17-x\right)=x+3\)
\(\Leftrightarrow x-17+x=x+3\)
\(\Leftrightarrow x+x-x=17+3\)
\(\Leftrightarrow x=20\)
b)\(-\left(x+12\right)+35=-47\)
\(\Leftrightarrow-x-12+35=-47\)
\(\Leftrightarrow-x=-47+12-35\)
\(\Leftrightarrow-x=-70\)
\(\Leftrightarrow x=70\)
c)\(15-\left(x+32\right)=-11\)
\(\Leftrightarrow15-x-32=-11\)
\(\Leftrightarrow-x=-11-15+32\)
\(\Leftrightarrow-x=6\)
\(\Leftrightarrow x=-6\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1
S₂ = 21 + 23 + 25 + ... + 1001
Số số hạng của S₂:
(1001 - 21) : 2 + 1 = 491
⇒ S₂ = (1001 + 21) . 491 : 2 = 250901
--------
S₄ = 15 + 25 + 35 + ... + 115
Số số hạng của S₄:
(115 - 15) : 10 + 1 = 11
⇒ S₄ = (115 + 15) . 11 : 2 = 715
Bài 2
a) 2x - 138 = 2³.3²
2x - 138 = 8.9
2x - 138 = 72
2x = 72 + 138
2x = 210
x = 210 : 2
x = 105
b) 5.(x + 35) = 515
x + 35 = 515 : 5
x + 35 = 103
x = 103 - 35
x = 78
c) 814 - (x - 305) = 712
x - 305 = 814 - 712
x - 305 = 102
x = 102 + 305
x = 407
d) 20 - [7.(x - 3) + 4] = 2
7(x - 3) + 4 = 20 - 2
7(x - 3) + 4 = 18
7(x - 3) = 18 - 4
7(x - 3) = 14
x - 3 = 14 : 7
x - 3 = 2
x = 2 + 3
x = 5
e) 9ˣ⁻¹ = 9
x - 1 = 1
x = 1 + 1
x = 2
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92 + 71 + 108 = (92 + 108) + 71 = 200 + 71 = 271
32 x 47 + 53 x 47 + 47 x 15 = 47(32 + 53 + 15)
= 47.100
= 4700
90 x 143 - 43 x 90 = 90.(143 - 43) = 90.100 = 9000
(1200 + 60) : 12 = 1800 : 12 = 150
2 x 18 x 24 + 3 x 50 x 16 + 12 x 32 x 4 = 18.(2.24) + 50.(3.16) + 32.(12.4) = 18.48 + 50.48 + 32.48 = 48(18 + 50 + 32) = 48.100 = 4800
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\(\text{35 + (–47) – |–12|}\)
\(=-12-12\)
\(=-24\)
\(\text{(–15) – 70 : (–14) + (–32) . (–2)}\)
\(=-15+5+64\)
\(=-10+64\)
\(=54\)
\(\text{ 15 – 12 . (-3)^2 – 135 : |–15|}\)
\(=15-12.9-135:15\)
\(=15-108-9\)
\(=-102\)
Tính hợp lý:
\(\text{ –24 . 78 + 24(–35) – 24(–13)}\)
\(=24.\left(-78+\left(-35\right)-\left(-13\right)\right)\)
\(=24.\left(-100\right)\)
\(=-2400\)
học tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
a/ x - ( 17 - x ) = x + 3
=> x - 17 + x = x + 3
=> 2. x - 17 = x + 3
=> 2. x - x = 3 + 17
=> x = 20
b/ - ( x + 12 ) + 35 = - 47
=> -x - 12 + 35 = -47
=> -x + 23 = -47
=> -x = -47 - 23 = -70
=> x = 70
c/ 15 - ( x + 32 ) = - 11
=> x + 32 = 15 - (-11) = 15 + 11 = 26
=> x = 26 - 32 = -6