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a) 310-(118-x)=217
118-x=310-217
118-x=93
x=118-93
x=25
b) 814-(x-305)=712
x-305=814-712
x-305=102
x =102+305
x = 407
c)5(x+35)=515
x+35 =515:5
x+35 =103
x =103-35
x =68
\(a,310-\left(118-x\right)=217\) \(c,5\left(x+35\right)=515\)
\(118-x=310-217\) \(x+35=515:5\)
\(118-x=93\) \(x+35=103\)
\(x=118-93\) \(x=103-35\)
\(x=25\) \(x=68\)
\(b,814-\left(x-305\right)=712\) \(\left[\left(6.x-39\right):3\right].28=5628\)
\(x-305=814-712\) \(\left(6.x-39\right):3=5628:28\)
\(x-305=102\) \(\left(6.x-39\right):3=201\)
\(x=102+305\) \(6.x-39=201x3\)
\(x=407\) \(6.x-39=603\)
\(6x=603+39\)
\(6x=642\)
\(x=107\)
\(e,2.x-138=2^3.2^2\)
\(2.x-138=32\)
\(2.x=32+138\)
\(2.x=170\)
\(x=170:2\)
\(x=85\)
(X-3)-120=0
X-123=0
X=123
8x-3=0
8x=3
x=3/8
124+(118-x)=217
118-x=93
x=25
156-(x+61)=82
x+61=74
x=13
814-(x-305)=712
x-305=102
x=407
(X-32)÷16=48
x-32=768
x=800
X-32: 16=48
x-2=48
x=50
( x - 3 ) - 120 = 0
<=> x - 3 = 120
<=> x = 120 + 3
<=> x = 123
8x - 3 = 0
<=> 8x = 3
<=> x = 3 : 8
<=> x = 3/8
124 + ( 118 - x ) = 217
<=> 118 - x = 217 - 124
<=> 118 - x = 93
<=> x = 118 - 93
<=> x = 25
156 - ( x + 61 ) = 82
<=> x + 61 = 156 - 82
<=> x + 61 = 74
<=> x = 74 -61
<=> x = 13
814 -( x - 305 ) = 712
<=> x - 305 = 814-712
<=> x - 305 = 102
<=> x =102 + 305
<=> x = 407
( x - 32) : 16 = 48
<=> x - 32 = 48 x 16
<=> x - 32 = 768
<=> x = 768 + 32
<=> x = 800
x - 32 : 16 = 48
<=> x - 2 = 48
<=> x = 48 + 2
<=> x = 50
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
a) (x-35)-120=0
x-35= 120
➩x = 155
b)310-(118-x)=217
118 -x = 93
➩ x = 25
c)156-(x+61)=82
➩ x + 61 = 74
➩ x = 13
a: Ta có: \(x-35-120=0\)
\(\Leftrightarrow x-155=0\)
hay x=155
b: Ta có: \(310-\left(118-x\right)=217\)
\(\Leftrightarrow118-x=93\)
hay x=25
c: Ta có: \(156-\left(x+61\right)=82\)
\(\Leftrightarrow x+61=74\)
hay x=13
a)
(x-35)-120=0
=>x-35=0+120
=>x-35=120
=>x=120-35
=>x=85
b)
124+(118-x)=217
=>118-x=217-124
=>118-x=93
=>x=118-93
=>x=25
c) 125-(x+61)=82
=>x+61=125-82
=>x+61=43
=>x= 43-61
=>x= -18
a)
(x-35)-120=0
=>x-35=0+120
=>x-35=120
=>x=120-35
=>x=85
b)
124+(118-x)=217
=>118-x=217-124
=>118-x=93
=>x=118-93
=>x=25
c) 125-(x+61)=82
=>x+61=125-82
=>x+61=43
=>x= 43-61
=>x= -18
a)(x-35)-120=0 b)124+(118-x)=217 c)156-(x+61)=82
x-35 = 0+120=120 118-x =217-124=93 x+61 = 156-82=74
x = 120+35=155 x = 118-93=25 x =74-61=13
suy ra x=155 suy ra x= 25 suy ra x=13
a) ( x - 35 ) - 120 = 0
<=> x - 35 = 120
<=> x = 155
b) 124 + ( 118 - x ) = 217
<=> 118 - x = 93
<=> x = 25
c) 156 - ( x + 61 ) = 82
<=> x + 61 = 74
<=> x = 13
a, (x - 35) - 120 = 0
=> x - 35 = 120
=> x = 155
b, 124 + (118 - x) = 217
=> 118 - x = 93
=> x = 25
c, 156 - (x + 61) = 82
=> x + 61 = 74
=> x = 13
\(a,x-35=120\\ x=120+35\\ x=155\\ b,118-x=310-217\\ 118-x=93\\ x=25\\ c,x+61=156-82\\ x+61=74\\ x=74-61\\ x=13\\ d,x-305=814-712\\ x-305=102\\ x=407\\ e,2x-138=72\\ 2x=72+138\\ 2x=210\\ x=105\\ g,x+35=515:5\\ x+35=103\\ x=68\)