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TM
4
19 tháng 8 2017
=1/1-1/2+1/2 -1/3+1/3-1/4....... 1/56 -1/57+1/57-1/58
= 1/1-1/58
= 57/58
18 tháng 8 2015
a) 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/x.(x+1) = 499/500
1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + .... + 1/x - 1/x+1 = 499/500
1 - 1/x+1 = 499/500
1/x+1 = 1 - 499/500
1/x+1 = 1/500
x + 1 = 500
x = 500 - 1
x = 499
b) 1/1.3 + 1/3.5 + 1/5.7 + .... + 1/x.(x+2) = 20/41
1/2 . [ 2/1.3 + 2/3.5 + 2/5.7 + ... + 2/x.(x+2) ] = 20/41
1/2 . [ 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ... + 1/x - 1/x+2 ] = 20/41
1/2 . [ 1 - 1/x+2 ) = 20/41
1 - 1/x+2 = 20/41 : 1/2
1 - 1/x+2 = 40/41
1/x+2 = 1 - 40/41
1/x+2 = 1/41
x + 2 = 41
x = 41 - 2
x = 39
PH
2
T
25 tháng 7 2018
\(a̸\)
\(\frac{3}{5}-\frac{1}{2}.x=\frac{1}{4}\)
\(\frac{1}{2}.x=\frac{3}{5}-\frac{1}{4}\)
\(\frac{1}{2}.x=\frac{7}{20}\)
\(\Rightarrow\frac{7}{10}\)
\(b̸\)
\(11,3+2\left[x-\frac{1}{3}\right]=\frac{25}{6}\)
\(2\left[x-\frac{1}{3}\right]=\frac{25}{6}-11,3\)
\(2\left[x-\frac{1}{3}\right]=\frac{-107}{15}\)
\(x-\frac{1}{3}=\frac{-107}{15}:2\)
\(x-\frac{1}{3}=\frac{-107}{30}\)
\(x=\frac{-107}{30}+\frac{1}{3}\)
\(x=\frac{-97}{30}\)
25 tháng 7 2018
\(a)\frac{3}{5}-\frac{1}{2}x=\frac{1}{4}\)
\(\implies\frac{1}{2}x=\frac{3}{5}-\frac{1}{4}\)
\(\implies\frac{1}{2}x=\frac{7}{20}\)
\(\implies x=\frac{7}{20}:\frac{1}{2}\)
\(\implies x=\frac{7}{10}\)
Vậy...
\(b) 11,3+2(x-\frac{1}{3})=\frac{25}{6}\)
\(\implies \frac{113}{10}+2x-2.\frac{1}{3}=\frac{25}{6}\)
\(\implies \frac{113}{10}+2x-\frac{2}{3}=\frac{25}{6}\)
\(\implies \frac{113}{10}+2x=\frac{25}{6}+\frac{2}{3}\)
\(\implies \frac{113}{10}+2x=\frac{29}{6}\)
\(\implies 2x=\frac{29}{6}-\frac{113}{10}\)
\(\implies 2x=\frac{-97}{15}\)
\(\implies x=\frac{-97}{30}\)
Vậy..
\(c)5x-435+2x+140+3x=565\)
\(\implies (5x+2x+3x)+(-435+140)=565\)
\(\implies 10x+(-295)=565\)
\(\implies 10x=565-(-295)\)
\(\implies 10x=860\)
\(\implies x=86\)
Vậy...
~ hok tốt a~
HC
1
16 tháng 6 2016
1) 31-3.(x+2) = 7
3.(x+2) = 31- 7
3.(x+2) = 24
x+2 = 24:3
x + 2 = 8
x = 8-2
x = 6
2) 175-25.(2x-1) = 175
25.(2x-1) = 175- 175 = 0
2x-1 = 0 : 25 = 0
2x = 0 + 1 = 1
x = 1 : 2 = 0,5
3) 25 - x/2 = 19
x/2 = 25-19
x/2 = 6
x : 2 = 6
x = 6 x 2 = 12
4) 2.(x-1)+3 = 15
2.(x-1) = 15 - 3 = 12
x - 1 = 12 : 2 = 6
x = 6+1 = 7
7 tháng 8 2017
a.\(\frac{11}{14}-\frac{3}{x-1}=\frac{5}{14}\)
\(\frac{3}{x-1}=\frac{11}{14}-\frac{5}{14}\)
\(\frac{3}{x-1}=\frac{3}{7}\)
\(\Rightarrow x-1=7\)
\(x=7+1\)
Vậy \(x=8\)
b.\(\frac{42}{25}:\frac{2x+1}{5}=\frac{6}{5}\)
\(\frac{2x+1}{5}=\frac{42}{25}:\frac{6}{5}\)
\(\frac{2x+1}{5}=\frac{7}{5}\)
\(\Rightarrow2x+1=7\)
\(2x=7-1\)
\(2x=6\)
\(x=6:2\)
\(x=3\)
HL
7 tháng 8 2017
a.\(\frac{11}{14}-\frac{3}{x-1}=\frac{5}{14}\)
\(\frac{3}{x-1}=\frac{11}{14}-\frac{5}{14}=\frac{3}{7}\)
\(\Rightarrow x-1=7\)
\(x=7+1=8\)
VẬY, \(x=8\)
b. \(\frac{42}{25}:\frac{2x+1}{5}=\frac{6}{5}\)
\(\frac{2x+1}{5}=\frac{42}{25}:\frac{6}{5}=\frac{7}{5}\)
\(\Rightarrow2x+1=7\)
\(2x=7-1=6\)
\(x=6:2=3\)
VẬY, \(x=3\)
9 tháng 9 2017
a) ( 2x - 25 ) : 3 = 27
( 2x - 25 ) = 81
2x = 81 + 25
2x = 106
x = 53
b) ( x - 3 ) ( 8 - x ) = 0
\(\Rightarrow\orbr{\begin{cases}x-3=0\\8-x=0\end{cases}}\)\(\Rightarrow\orbr{\begin{cases}x=3\\x=8\end{cases}}\)
d) 516 - ( 246 + 3x ) = 26
246 + 3x = 490
3x = 244
x =
9 tháng 9 2017
a)(2x - 25) : 3 = 27
=> 2x - 25 = 27 . 3
=> 2x - 25 = 81
=> 2x = 81 + 25 = 106
=> x = 106 : 2 = 53
b)(x - 3).(8 - x) = 0
=> x - 3 = 0 hoặc 8 - x = 0
=> x = 3 hoặc x = 8
c) 889 - 5x - 2x = 375
=>889 - 7x = 375
=>7x = 889 - 375
=>7x = 514
=>x = 514/7
d) 516 - ( 246 + 3x ) = 26
=> 246 + 3x = 516 - 26
=> 246 + 3x = 490
=> 3x = 490 - 246
=> 3x = 244
=> x = 244/3
e) x + 1 + 2 + 3 + ... + 50 = 1500
=>x + (1 + 2 + 3 + ... + 50) = 1500
=>x + 50.(50+1):2 = 1500
=>x + 1275 = 1500
=>x = 1500 - 1275
=>x = 225
a) \(2^x=16\)
\(\Rightarrow2^x=2^4\)
\(\Rightarrow x=4\)
b) \(9^{x-1}=9\)
\(\Rightarrow9^{x-1}=9^1\)
\(\Rightarrow x-1=1\)
\(\Rightarrow x=1+1\)
\(\Rightarrow x=2\)
c) \(x^4=16\)
\(\Rightarrow x^4=2^4\)
\(\Rightarrow x=2\)
d)\(2^x:2^5=1\)
\(\Rightarrow2^{x-5}=2^0\)
\(\Rightarrow x-5=0\)
\(\Rightarrow x=5\)
a) 2x = 16
<=> 2x = 24
<=> x = 4
=> x = 4
b) 9x - 1 = 9
<=> 9x - 1 = 91
<=> x - 1 = 1
<=> x = 2
=> x = 2
c) x4 = 16
<=> x4 = 24
<=> x = -2; 2
=> x = -2; 2