Question

Cmr:

A= \(\dfrac{3}{1^2×2^2}\)+\(\dfrac{5}{2^2×3^2}\)+\(\dfrac{7}{3^2×4^2}\)+...+\(\dfrac{4031}{2015^2×2016^2}\)<1

Answer 1

\(A=\dfrac{3}{1^2.2^2}+\dfrac{5}{2^2.3^2}+\dfrac{7}{3^2.4^2}+...+\dfrac{4031}{2015^2.2016^2}\)

\(A=\dfrac{2^2-1^2}{1^2.2^2}+\dfrac{3^2-2^2}{2^2.3^2}+\dfrac{4^2-3^2}{3^2.4^2}+...+\dfrac{2016^2-2015^2}{2015^2.2016^2}\)

\(A=1-\dfrac{1}{2^2}+\dfrac{1}{2^2}-\dfrac{1}{3^2}+\dfrac{1}{3^2}-\dfrac{1}{4^2}+...+\dfrac{1}{2015^2}-\dfrac{1}{2016^2}\)

\(A=1-\dfrac{1}{2016^2}< 1\left(đpcm\right)\)