Bài 4 : Tìm STN x , biết :
a) ( x - 35 ) - 120 = 0
b) 310 - ( 118 - x ) = 217
c) 156 - ( x + 61 ) = 82
d) 814 - ( x - 305 ) = 712
e) 2x - 138 = 23 . 32
g) 5 ( x + 35 ) = 515
h) 20 - [ 7 ( x - 3 ) + 4 ] = 2
i) [ ( 6x - 39 ) : 3 ] . 28 = 5628
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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
\(a,310-\left(118-x\right)=217\) \(c,5\left(x+35\right)=515\)
\(118-x=310-217\) \(x+35=515:5\)
\(118-x=93\) \(x+35=103\)
\(x=118-93\) \(x=103-35\)
\(x=25\) \(x=68\)
\(b,814-\left(x-305\right)=712\) \(\left[\left(6.x-39\right):3\right].28=5628\)
\(x-305=814-712\) \(\left(6.x-39\right):3=5628:28\)
\(x-305=102\) \(\left(6.x-39\right):3=201\)
\(x=102+305\) \(6.x-39=201x3\)
\(x=407\) \(6.x-39=603\)
\(6x=603+39\)
\(6x=642\)
\(x=107\)
\(e,2.x-138=2^3.2^2\)
\(2.x-138=32\)
\(2.x=32+138\)
\(2.x=170\)
\(x=170:2\)
\(x=85\)
1) (x - 35) - 120 = 0
x - 35 = 120
x = 120 + 35
x = 155
2) 310 - (118 - x) = 217
118 - x = 310 - 217
118 - x = 93
x = 118 - 93
x = 25
3) 156 - (x + 61) = 82
x + 61 = 156 - 82
x + 61 = 74
x = 74 - 61
x = 13
4) 814 - (x - 305) = 712
x - 305 = 814 - 712
x - 305 = 102
x = 102 + 305 = 407
5) 100 - 7 - (x - 5) = 58
x - 5 = 93 - 58
x - 5 = 35
x = 35 + 5 = 40
6) 12(x - 1) : 3 = 43 + 23
4(x - 1) = 72
x - 1 = 18
x = 18 + 1 = 19
7) 24 + 5x = 75 : 73
24 + 5x = 49
5x = 25
x = 25 : 5 = 5
8) 5(x - 1) : 3 = 43 + 23
\(\dfrac{5}{3}\left(x-1\right)=72\)
x - 1 = \(\dfrac{216}{5}\)
x = 221/5
9) 5(x - 4)2 - 7 = 13
5(x - 4)2 = 20
(x - 4)2 = 4
\(\Rightarrow\left[{}\begin{matrix}x-4=2\\x-4=-2\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x=6\\x=2\end{matrix}\right.\)
10) (x + 1) + (x + 2) + ... + (x + 30) = 795
=> (x + x + x + ... + x) + (1 + 2 + 3 +...+ 30) = 795 (1)
Đặt A = 1 + 2 + 3 +...+ 30
Số số hạng trong A là: (30 - 1) : 1 + 1 = 30 (số)
Tổng A bằng : (30 + 1).30 : 2 =465
Thay A = 465 vào (1) , ta được:
30x + 465 = 795
=> 30x =330
=> x =11
1: =>x-35=120
=>x=120+35=155
2: =>118-x=310-217=93
=>x=118-93=25
3: =>x+61=156-82=74
=>x=74-61=13
4: =>x-305=814-712=102
=>x=102+305=407
5: =>93-(x-5)=58
=>x-5=35
=>x=40
6: =>4(x-1)=64+8=72
=>x-1=18
=>x=19
7: =>5x+24=49
=>5x=25
=>x=5
8: =>5(x-1):3=4^3+2^3=64+8=72
=>5(x-1)=216
=>x-1=216/5
=>x=221/5
(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
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
( x - 1 ) + 5 = 17
x - 1 = 17 - 5
x - 1 = 12
x = 12 + 1
x = 13
\(a,x-35=120\\ x=120+35\\ x=155\\ b,118-x=310-217\\ 118-x=93\\ x=25\\ c,x+61=156-82\\ x+61=74\\ x=74-61\\ x=13\\ d,x-305=814-712\\ x-305=102\\ x=407\\ e,2x-138=72\\ 2x=72+138\\ 2x=210\\ x=105\\ g,x+35=515:5\\ x+35=103\\ x=68\)