a: \(=\dfrac{-3}{10}\left(-\dfrac{5}{7}+\dfrac{5}{11}+\dfrac{-2}{7}+\dfrac{6}{11}\right)=0\)
b: P=1+1/2+...+1/2^99+2/2^100
=1+1/2+...+2/2^99
=...
=1+2/2
=2
c: \(=\dfrac{2^2-1+1}{\left(2-1\right)\left(2+1\right)}\cdot\dfrac{3^2-1+1}{\left(3-1\right)\left(3+1\right)}\cdot...\cdot\dfrac{2015^2-1+1}{\left(2015-1\right)\left(2015+1\right)}\)
\(=\dfrac{2}{1}\cdot\dfrac{3}{2}\cdot...\cdot\dfrac{2015}{2014}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot...\cdot\dfrac{2015}{2016}\)
=2015/1*2/2016=2015/1008
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