CMR A< $\frac{1}{4}$ biết A= $\frac{1}{1.2.3}$+$\frac{1}{2.3.4}$+..+$\frac{1}{2014.2015.2016}$ help me! thank nhìu

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1. A=1/2.(2/1.2.3+2/2.3.4+2/3.4.5+…+2/2014.2015.2016)

   A=1/2.(1/1.2-1/2.3+1/3.4+1/4.5+1/5.6+…+1/2014.2015-1/2015.2016)

   A=1.2(1/2-1/2015.2016)

    A<1/1.2/2=1/4

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