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a,3,25+0,9-x=0,97
4,15-x=0,97
x=4,15-0,97
x=3,18
b,4,4-9,2+x=1,2
-4,8+x=1,2
x=1,2-(-4,8)
x=6
c,7/5+x-2/5=4
7/5+x=4+2/5
7/5+x=22/5
x=22/5-7/5
x=15/5
x=3
d,1 3/4+x-7/8=5
7/4+x-7/8=5
7/4+x=5+7/8
7/4+x=47/8
x=47/8-7/4
x=47/8-14/8
x=33/8
a,3,25+0,9-x=0,97
4,15-x=0,97
x=4,15-0,97
x=3,18
b,4,4-9,2+x=1,2
-4,8+x=1,2
x=1,2-(-4,8)
x=6
c,7/5+x-2/5=4
7/5+x=4+2/5
7/5+x=22/5
x=22/5-7/5
x=15/5
x=3
d,1 3/4+x-7/8=5
7/4+x-7/8=5
7/4+x=5+7/8
7/4+x=47/8
x=47/8-7/4
x=47/8-14/8
x=33/8

Bài 2:
3,15*x+1,35*x=2,7
x*(3,15+1,35)=2,7
x*4,5=2,7
x=2,7:4,5
x=0,6

a) \(38,7\times\left(38,7-x\right)=38,7\)
\(38,7-x=38,7:38,7\)
\(38,7-x=1\)
\(x=38,7-1\)
\(x=37,7\)

a. 420 : (x : 39) = 105
x : 39 = 420 : 105
x : 39 = 4
x = 4 x 39
x = 156
b. 200 - 18 : (372 : 3 : x - 1) - 28 = 166
200 - 28 - 166 = 18 : (372 : 3 : x - 1)
6 = 18 : (124 : x - 1)
18 : (124 : x - 1) = 6
124 : x - 1 = 18 : 6
124 : x - 1 = 3
124 : x = 4
x = 124 : 4
x = 31
c. 429 : (x + 31) = 11
x + 31 = 429 : 11
x + 31 = 39
x = 39 - 31
x = 8
d. 1615 : (X x 19) = 17
X x 19 = 1615 : 17
X x 19 = 95
X = 95 : 19
X = 5
cho mình xin tick nhé !
a: 420:(x:39)=105
=>\(x:39=420:105=4\)
=>\(x=4\times39=156\)
b: \(200-18:\left(372:3:x-1\right)-28=166\)
=>\(172-18:\left(124:x-1\right)=166\)
=>\(18:\left(124:x-1\right)=172-166=6\)
=>\(124:x-1=18:6=3\)
=>\(124:x=3+1=4\)
=>\(x=\frac{124}{4}=31\)
c: \(429:\left(x+31\right)=11\)
=>x+31=429:11=39
=>x=39-31=8
d: \(1615:\left(x\times19\right)=17\)
=>\(x\times19=1615:17=95\)
=>x=95:19=5

a. 2x.4=128
2x =32
=> x = 5
b. 2x+1=125
2x = 125-1
2x = 124
x = 62
c. x15=x
=> x \(\in\left\{0;\pm1\right\}\)

a ) ( x + 74 ) - 318 = 200
x + 74 = 200 + 318
x + 74 = 518
x = 518 - 74
x = 444
b ) 3636 : ( 12 . x - 91 ) = 36
12 . x - 91 = 3636 : 36
12 . x - 91 = 101
12 . x = 101 + 91
12 . x = 192
x = 192 : 12
x = 16
c ) ( x : 23 + 45 ) . 67 = 8911
x : 23 + 45 = 8911 : 67
x : 23 + 45 = 133
x : 23 = 133 - 45
x : 23 = 88
x = 88 . 23
x = 2024
d ) ( 3 . x - 6 ) + 57 = 60
3 . x - 6 = 60 - 57
3 . x - 6 = 3
3 . x = 3 + 6
3 . x = 9
x = 9 : 3
x = 3
\(a)\) \(\left(x+74\right)-318=200\)
\(x+74=518\)
\(x=444\)
Vậy x = 444
\(b)\) \(3636:\left(12x-91\right)=36\)
\(12x-91=101\)
\(12x=192\)
\(x=16\)
Vậy x = 16
\(c)\) \(\left(x:23+45\right)67=8911\)
\(x:23+45=133\)
\(x:23=88\)
\(x=2024\)
Vậy x = 2024
\(d)\left(3x-6\right)+57=60\)
\(3x-6=3\)
\(3x=9\)
\(x=3\)
Vậy x = 3

A.1/2x3 +1/3x4 +1/4x5+...+1/99x100
=1/2 -1/3 +1/3-1/4+1/4-1/5+...+1/99-1/100
=1/2-1/100
=49/100

Đáp án B