Tính giá trị biểu thức: A’=’ ‘4/1.2’ ‘+’ ‘4/2.3’ ‘+’ 4/3.4′ ‘+’ …. ‘+’ ‘4/2014.2015’

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1. A’=’ ‘4/1.2’ ‘+’ ‘4/2.3’ ‘+’ 4/3.4′ ‘+’ …. ‘+’ ‘4/2014.2015’

   A=4.(1/1.2’+ ‘1/2.3’ ‘+’ 1/3.4′ ‘+’ …. ‘+’ ‘1/2014.2015’

    A=4.(1-1/2+1/2-1/3+1/3-1/4+…..-1/2014+1/2014-1/2015)

   A=4.(1-1/2015)

   A=4.2014/2015

   A=8056/2015

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2. `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}`

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