`A=\frac{4}{1.2}+``\frac{4}{2.3}``+\frac{4}{3.4}+``...+\frac{4}{2014.2015}`
`⇒` `A=\4.(frac{1}{1.2}+``\frac{1}{2.3}``+\frac{1}{3.4}+``...+\frac{1}{2014.2015})`
`⇒` `A=\4.(frac{1}{1}-``\frac{1}{2}``+\frac{1}{2}-``\frac{1}{3}+``\frac{1}{3}``-``\frac{1}{4}``...+\frac{1}{2014}` `-` `\frac{1}{2015})`
`⇔` `A=``\4.(frac{1}{1}` `-` `\frac{1}{2015})`
`⇒` `A=` `4.\frac{2014}{2015}`
`⇒` `A=` `\frac{8056}{2015}`
Vậy `:` `A` `=` `\frac{8056}{2015}`
