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HT
0
LA
2
M
20 tháng 7 2017
ta có : x+3/5+x+4/5=x+5/3+x+6/2
=> (x+x)+(3/5+4/4)=(x+x)+(5/3+6/2)
=> 2x+8/5=2x+14/3 ( vô lí )
HH
20 tháng 7 2017
Ta có: \(x+\frac{3}{5}+x+\frac{4}{4}=x+\frac{5}{3}+x+\frac{6}{2}\)
=> \(x+\frac{3}{5}+x+1=x+\frac{5}{3}+x+3\)
=> \(x+1+x+3=x+\frac{5}{3}-x-\frac{3}{5}\)
=> \(2x+4=\frac{25-9}{15}\)
=> \(2x+4=\frac{16}{15}\)
=> \(2x+4=1+\frac{1}{15}\)
=> \(2x+4-1=\frac{1}{15}\)
=> \(2x+3=\frac{1}{15}\)
=> \(2x=\frac{1}{15}-3\)
=> \(2x=\frac{1-45}{15}\)
=> \(2x=-\frac{44}{15}\)
=> \(x=\frac{\left(-\frac{44}{15}\right)}{2}\)
=> \(x=-\frac{44}{15}.\frac{1}{2}\)
=> \(x=-\frac{22}{15}\)
LN
1
31 tháng 5 2020
(x+1)+(x+2)+(x+3)+...+(x+100)=2020
x+1+x+2+x+3+...+x+100=2020
(x+x+x+...+x)+(1+2+3+...+100)=2020
100x+5050=2020
100x=2020-5050
100x=-3030
x=-30,3
18 tháng 1 2022
Bài 1:
a: \(\dfrac{25}{42}-\dfrac{20}{63}=\dfrac{75-40}{126}=\dfrac{35}{126}=\dfrac{5}{18}\)
b: \(\dfrac{9}{20}-\dfrac{13}{75}-\dfrac{1}{6}=\dfrac{135}{300}-\dfrac{52}{300}-\dfrac{50}{300}=\dfrac{33}{300}=\dfrac{11}{100}\)
A
1
27 tháng 4 2017
Ta có : \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+1\right)\div2}=\frac{2009}{2011}\)
Đặt tổng vế trái là A
Ta có : \(A=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+1\right)\div2}\)
\(\frac{1}{2}A=\frac{1}{2}\left(\frac{1}{3}+\frac{1}{6}+...+\frac{1}{x\left(x+1\right)\div2}\right)\)
\(\frac{1}{2}A=\frac{1}{6}+\frac{1}{12}+...+\frac{1}{x\left(x+1\right)}\)
\(\frac{1}{2}A=\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x\left(x+1\right)}\)
\(\frac{1}{2}A=\left(\frac{1}{2}-\frac{1}{3}\right)+\left(\frac{1}{3}-\frac{1}{4}\right)+...+\left(\frac{1}{x}-\frac{1}{x+1}\right)\)
\(\frac{1}{2}A=\frac{1}{2}-\frac{1}{x+1}\)
\(A=\left(\frac{1}{2}+\frac{1}{x+1}\right):\frac{1}{2}\)
\(A=1+\frac{1}{\left(x+1\right)\div2}\)
\(\Rightarrow1+\frac{1}{\left(x+1\right)\div2}=\frac{2009}{2011}\)
\(\Rightarrow\frac{1}{\left(x+1\right)\div2}=\frac{2009}{2011}-1=\frac{2009}{2011}-\frac{2011}{2011}=-\frac{2}{2011}\)
\(\Rightarrow-\frac{2}{-\left(x+1\right)}=-\frac{2}{2011}\)
\(\Rightarrow-\left(x+1\right)=2011\)
\(\Rightarrow x+1=-2011\)
\(\Rightarrow x=-2011-1=-2012\)
28 tháng 4 2023
a: 3x-2=2x-3
=>x=-1
b: 2x+3=5x+9
=>-3x=6
=>x=-2
c: 5-2x=7
=>2x=-2
=>x=-2
d: 10x+3-5x=4x+12
=>5x+3=4x+12
=>x=9
e: 11x+42-2x=100-9x-22
=>9x+42=78-9x
=>18x=36
=>x=2
f: 2x-(3-5x)=4(x+3)
=>2x-3+5x=4x+12
=>7x-3=4x+12
=>3x=15
=>x=5
ta có:
\(1+2+3+....+x=210\)
\(\Rightarrow\frac{\left(x+1\right).\left(x-1+1\right)}{2}=210\)
\(\Rightarrow\left(x+1\right).x=420\)
ta có: \(20.21=420\Rightarrow x=20\)
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