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18 tháng 4 2016

giúp mk mk tích cho

18 tháng 4 2016

A=10(1/1.2+5/2.3+...+89/9.10)

A=10(1/2+5/6+...+89/90)

A=10[(1-1/2)+(1-1/6)+.....+(1-1/90)

A=10(1-1/2+1-1/6+...+1-1/90)

A=10[(1+1+...+1)-(1/2+1/6+...+1/90)

           9 chữ số 1

A=10[9-(1/1.2+1/2.3+...+1/9.10)]

A=10[9-(1-1/2+1/2-1/3+...+1/9-1/10)]

A=10[9-(1-1/10)]

A=10(9-9/10)

A=90-9=81

18 tháng 8 2019

\(\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{9\cdot10}\right)\cdot100-\left[\frac{5}{2}:\left(X+\frac{206}{100}\right)\right]:\frac{1}{2}=89\\ \left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\right)\cdot100-\left[\frac{5}{2}:\left(X+\frac{206}{100}\right)\right]:\frac{1}{2}=89\\ \left(1-\frac{1}{10}\right)\cdot100-\left[\frac{5}{2}:\left(X+\frac{206}{100}\right)\right]:\frac{1}{2}=89\\ \frac{9}{10}\cdot100-\left[\frac{5}{2}:\left(X+\frac{206}{100}\right)\right]:\frac{1}{2}=89\\ 90-\left[\frac{5}{2}:\left(X+\frac{206}{100}\right)\right]:\frac{1}{2}=89\\ \left[\frac{5}{2}:\left(X+\frac{206}{100}\right)\right]:\frac{1}{2}=1\\ \frac{5}{2}:\left(X+\frac{206}{100}\right)=\frac{1}{2}\\ X+\frac{206}{100}=5\\ X=\frac{500}{100}-\frac{206}{100}\\ X=\frac{294}{100}=\frac{147}{50}\)

Vậy \(X=\frac{147}{50}\)

18 tháng 8 2019

( 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ......+ 1/9 - 1/10) . 100 - [ 5/2 : ( x + 103/50 ) ] = 89 . 1/2

( 1 - 1/10) . 100 - [ 5/2 : ( x + 103/50 ) ] = 89/2

90 - 5/2 : ( x + 103/50 ) = 89/2

5/2 : ( x + 103/50 ) = 90 - 89/2

5/2 : ( x + 103/50 ) = 91/2

x + 103/50 = 5/2 : 91/2

x + 103/50 = 5/91

x = 5/91 - 103/50

x = -9,123/4550

2 tháng 2 2016

\(\text{Đề }\Leftrightarrow\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\right).\left(x-1\right)=x-\frac{1}{3}\)

=> \(\left(1-\frac{1}{10}\right).\left(x-1\right)=x-\frac{1}{3}\)

=> \(\frac{9}{10}.\left(x-1\right)=x-\frac{1}{3}\)

=> \(\frac{9x}{10}-\frac{9}{10}=\frac{3x-1}{3}\)

=> \(\frac{27x}{30}-\frac{27}{30}=\frac{10.\left(3x-1\right)}{30}\)

=> 27x - 27 = 30x - 10

=> 27x - 30x = -10 + 27

=> -3x = 17

=> x = -17/3.

12 tháng 5 2019

A = 10.(1/1.2+5/2.3+...+89/9.10)

A/10 = 1/1.2+5/2.3+...+89/9.10

1.9 - A/10 = (1 - 1/1.2) + (1 - 5/2.3) +...+ (1 - 89/9.10)

9 - A/10 = 1/1.2 + 1/2.3 +....+ 1/9.10

9 - A/10 = 1 - 1/2 +1/2 -1/3 +...+ 1/9 -1 /10

9 - A/10 = 1 +0 +0+...... + 0 - 1/10

9 - A/10 = 1- 1/10

9 - A/10 = 9/10

A/10 = 9 - 9/10

A/10 = 81/10

A = (81/10) . 10

A = 81.

Vậy A = 81

12 tháng 5 2019

Ta có : \(A=10\left(\frac{1}{1.2}+\frac{5}{2.3}+...+\frac{89}{9.10}\right)\)

\(\Rightarrow10\left(\frac{1}{2}+\frac{5}{6}+...+\frac{89}{90}\right)\)

\(\Rightarrow10\left[\left(1-\frac{1}{2}\right)+\left(1-\frac{1}{6}\right)+...+\left(1-\frac{1}{90}\right)\right]\)

\(\Rightarrow10\left[9-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{90}\right)\right]\)

\(\Rightarrow10\left[9-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{9.10}\right)\right]\)

\(\Rightarrow10\left[9-\frac{9}{10}\right]\)

\(\Rightarrow10.\frac{81}{10}\)

\(\Rightarrow A=81\)

~\(Study\) \(well\)~

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