Question

A=1/2.5+1/5.8+1/8.11+...+1/92.95+1/95.98

Answer 1

3A = \(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{92.95}+\frac{3}{95.98}\)

3A=\(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{95}-\frac{1}{98}\)

3A=\(\frac{1}{2}-\frac{1}{98}\)

3A=\(\frac{98}{196}-\frac{2}{196}\)=\(\frac{96}{196}=\frac{24}{49}\)

A=\(\frac{24}{49}:3=\frac{24}{49}.\frac{1}{3}=\frac{8}{49}\)

Vậy A = \(\frac{8}{49}\)

Answer 2

\(A=\frac{1}{2\cdot5}+\frac{1}{5\cdot8}+\frac{1}{8\cdot11}+...+\frac{1}{92\cdot95}+\frac{1}{95\cdot98}\)

\(\Rightarrow3A=3\left(\frac{1}{2\cdot5}+\frac{1}{5\cdot8}+\frac{1}{8\cdot11}+...+\frac{1}{92\cdot95}+\frac{1}{95\cdot98}\right)\)

\(\Rightarrow3A=\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+...+\frac{3}{92\cdot95}+\frac{3}{95\cdot98}\)

\(\Rightarrow3A=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{92}-\frac{1}{95}+\frac{1}{95}-\frac{1}{98}\)

\(\Rightarrow3A=\frac{1}{2}-\frac{1}{98}\)

\(\Rightarrow3A=\frac{24}{49}\)

\(\Rightarrow A=\frac{24}{49}:3\)

\(\Rightarrow A=\frac{8}{49}\)

Vậy \(A=\frac{8}{49}\)

Answer 3

\(A=3.\left(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{95.98}\right)\)

\(=3.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{95}-\frac{1}{98}\right)\)

\(=3.\left(\frac{1}{2}-\frac{1}{98}\right)\)

\(=3.\frac{24}{49}\)

\(=\frac{72}{49}\)

Answer 4

3A=3/2.5+3/5.8+...+3/92.95+3/95.98

3A=1/2-1/5+1/5-1/8+1/8-1/11+...+1/92-1/95+1/95-1/98

3A=1/2-1/98

3A=24/49

A=8/49

Answer 5

3A = \(3\left(\frac{1}{2.5}+\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{92.95}+\frac{1}{95.98}\right)\)

3A = \(\frac{3}{2.5}+\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{92.95}+\frac{3}{95.98}\)

3A = \(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{92}-\frac{1}{95}+\frac{1}{95}-\frac{1}{98}\)

3A = \(\frac{1}{2}-\frac{1}{98}\)

3A = \(\frac{24}{49}\)

\(\Rightarrow\)A = \(\frac{8}{49}\)

Vậy A = \(\frac{8}{49}.\)

Answer 6

ta có 

1/2.5 + 1/5.8 + 1/8.11 + .... + 1/95.98   

= ( 3/2.5 + 3/5.8 + 3/8.11 + ..... + 3/95.98 ) /3 

= ( 1/2 -1/5 +1/5 -1/8 +1/8 - 1/11 + ...... - 1/98 ) /3

= ( 1/2 -1/98 ) /3

=  (24/49 ) /3

=   72/49

nhớ k cho mn nhé !

Answer 7

A=1/3(3/2.5+3/5.8+3/8.11+3/11.14+...+3/95.98)

=1/3(1/2.5+1/5.8+1/8.11+...+1/95.98)

=1/3(1/2-1/5+1/5-1/8+1/8-...+1/95-1/98)

=1/3(1/2-1/98)

=1/3.24/49=8/49

Answer 8

đề bài sai bạn ơi