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a. 12,5 - \(x\) = \(x\) + 12
\(x\) + 12 + \(x\) = 12,5
\(x\) x 1 + \(x\) x 1 = 12,5 - 12
\(x\) x (1 + 1) = 0,5
\(x\) x 2 = 0,5
\(x\) = 0,5 : 2
\(x\) = 0,25
b, 8 \(\times\) \(x\) + 3 \(\times\) \(x\) + 2 \(\times\) \(x\) = 20
\(x\) \(\times\) (8 + 3 + 2) =20
\(x\) \(\times\) 13 = 20
\(x\) = 20 : 13
\(x\) = \(\dfrac{20}{13}\)
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a, (17x-25):8=81-65
(17x-25):8=16
17x-25=16:8
17x-25=2
17x=2+25
17x=27
x=27:17
x=27/17
b,720:[41-(2x-5)]=40
41-(2x-5)=720:40
41-(2x-5)=18
2x-5=41-18
2x-5=23
2x=23+5
2x=28
x=28:2
x=14
c,231-(x-6)=103
x-6=231-103
x-6=128
x=128+6
x=134
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đề bài: (17x-25):8+65= 81
(17x-25):8=81-65=16
17x-25= 16 . 8= 128
17x = 128+25=153
x = 153:17=9
b, Đề bài 720:[41-(2x-5)]=8.5
720:[41-(2x-5)]=40
41-(2x-5)=720:40=18
2x-5=41-18=23
2x = 23+5=28
x = 28:2= 14
c, 231-(x-6)=1339:13=103
x-6=231-103=128
x= 128 + 6= 134
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a) \(215+x=400\)
\(\Rightarrow x=400-215\)
\(\Rightarrow x=185\)
b) \(12,5-2x=\dfrac{1}{5}\)
\(\Rightarrow2x=12,5-\dfrac{1}{5}\)
\(\Rightarrow2x=\dfrac{123}{10}\)
\(\Rightarrow x=\dfrac{123}{10}:2\)
\(\Rightarrow x=\dfrac{123}{20}\)
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\(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+.......+\dfrac{1}{x\cdot\left(x+1\right)}=\dfrac{122}{123}\)
\(\Leftrightarrow1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+......+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{122}{123}\)
\(\Leftrightarrow1-\dfrac{1}{x+1}=\dfrac{122}{123}\)
\(\Leftrightarrow\dfrac{1}{x+1}=\dfrac{1}{123}\)
\(\Leftrightarrow x=122\)
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x*12,5 -x +x *2,75=1050
x*12,5 -x*1+x*2,75=`1050
x*(12,5-1+2,75)=1050
x*14,25=1050
x=1050:14,25
x= 73,68421053
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(18+38+16*76-1)=(36*19+64*20-65)-x
=>(18+38+1216-1)=(684+1280-65)-x
=>1271=1899-x
=>1899-x=1271
x = 1899-1271
x=628
vậy x= 628
( 18 + 38 + 1216 - 1) = ( 684 +1280 - 65) - x
( 56 + 1216 - 1) = ( 1964 - 65) - x
1271 = 1899 - x
x = 1899 - 1271
x = 628
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(375,4 . 12,5 - 27,5 : 2,75) . (24,8 : 0,25 - 49,6 . 2)
=(375,4 . 12,5 - 27,5 : 2,75) . (99,2-99,2)
= (375,4 . 12,5 - 27,5 : 2,75) . 0
=0
a, 41 - 12,5 x 3 = 85,5
b, 26,5 x 4,8 : 3 = 42,4