Question

\(a=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}.....+\frac{7}{69.70}\)

Answer 1

\(A=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)

\(A=7.\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+...+\frac{1}{69}-\frac{1}{70}\right)\)

\(A=7.\left(\frac{1}{10}-\frac{1}{70}\right)\)

\(A=7.\frac{3}{35}\)

\(A=\frac{3}{5}\)

Answer 2

a = 7/10 x 11 + 7/11 x 12 + 7/12 x 13 + .....+ 7/69 x 70

a = 7/10 - 7/11 + 7/11 - 7/12 + 7/12 - 7/13 + 7/13 - ......+7/69 - 7/70

a= 7/10 - 7/70

a = 3/5

Answer 3

\(A=7.\left(\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}+...+\frac{1}{69.70}\right)\)

suy ra \(A=7.\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+...+\frac{1}{69}-\frac{1}{70}\right)\)

\(A=7.\left(\frac{1}{10}-\frac{1}{70}\right)\)

\(A=7.\left(\frac{7}{70}-\frac{1}{70}\right)\)

\(A=7.\frac{6}{70}\)

\(A=\frac{3}{5}\)

Answer 4

A=7/10.11+7/11.12+7/12.13+...+7/69.70

=> A = 7.(1/10.11+1/11.12+...+1/69.70)

=> A= 7. ( 1/10-1/11+1/11-1/12+...+1/69-1/70)

=> A = 7.( 1/10 - 1/70 )

=> A = 7.3/35

=> A= 3/5

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Answer 5

\(A=\frac{7}{10.11}+\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)

\(A=7.\left(\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}+\frac{1}{12}-\frac{1}{13}+...+\frac{1}{69}-\frac{1}{70}\right)\)

\(A=7.\left(\frac{1}{10}-\frac{1}{70}\right)\)

\(A=7.\frac{3}{35}\)

\(A=\frac{3}{5}\)

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Answer 6

A = \(\frac{7}{10}-\frac{7}{11}+\frac{7}{11}-\frac{7}{12}+\frac{7}{12}-\frac{7}{13}+...+\frac{7}{69}-\frac{7}{70}\)

A = \(\frac{7}{10}-\frac{7}{70}\)

A = \(\frac{3}{5}\)

Answer 7

A=\(\frac{7}{10.11}\)+\(\frac{7}{11.12}+\frac{7}{12.13}+...+\frac{7}{69.70}\)

7A=\(\frac{1}{10.11}+\frac{1}{11.12}+\frac{1}{12.13}+....+\frac{1}{69.70}\)

7A=\(\frac{1}{10}.\frac{1}{11}+\frac{1}{11}.\frac{1}{12}+\frac{1}{12}.\frac{1}{13}+...+\frac{1}{68}.\frac{1}{69}+\frac{1}{69}.\frac{1}{70}\)

7A=\(\frac{1}{10}.\frac{1}{70}\)

7A=\(\frac{1}{700}\)

=>A=\(\frac{1}{700}:7\)

A=\(\frac{1}{4900}\)

Answer 8

A=7/10.11+7/11.12+7/12.13+...+7/69.70

=> A = 7.(1/10.11+1/11.12+...+1/69.70)

=> A= 7. ( 1/10-1/11+1/11-1/12+...+1/69-1/70)

=> A = 7.( 1/10 - 1/70 )

=> A = 7.3/35

=> A= 3/5