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b: \(=\dfrac{2014\cdot2015^2+2014\cdot2016-2016\cdot2015^2+2016\cdot2014}{2014\cdot2013^2-2014\cdot2012-2012\cdot2013^2-2012\cdot2014}\)
\(=\dfrac{2015^2\cdot\left(-2\right)+2\cdot\left(2015^2-1\right)}{2013^2\cdot\left(-2\right)-2\cdot\left(2013^2-1\right)}\)
\(=\dfrac{\left(-2\right)\cdot\left(2015^2-2015^2+1\right)}{\left(-2\right)\cdot\left(2013^2+2013^2-1\right)}=\dfrac{1}{2\cdot2013^2}\)
\(C=\dfrac{2014\left(2015^2+2016\right)-2016\left(2015^2-2014\right)}{2014\left(2013^2-2012\right)-2012\left(2013^2+2014\right)}\)
\(=\dfrac{2.2014.2016+2014.2015^2-2016.2015^2}{2014.2013^2-2012.2013^2-2.2012.2014}\)
\(=\dfrac{2.\left(2015+1\right)\left(2015-1\right)-2.2015^2}{2.2013^2-2.\left(2013+1\right)\left(2013-1\right)}\)
\(=\dfrac{2.\left(2015^2-1\right)-2.2015^2}{2.2013^2-2.\left(2013^2-1\right)}=\dfrac{-2}{2}=-1\)
Xét Tử số của A ta có:
\(2014+\frac{2013}{2}+\frac{2012}{3}+....+\frac{2}{2013}=1+\left(\frac{2013}{2}+1\right)+\left(\frac{2012}{3}+1\right)+....+\left(\frac{1}{2014}+1\right)\)\(TS=\frac{2015}{2}+\frac{2015}{3}+....+\frac{2015}{2014}+\frac{2015}{2015}\)
\(TS=2015.\left(\frac{1}{2}+\frac{1}{3}+....+\frac{1}{2015}\right)\)
\(A=\frac{2015.\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2015}\right)}{\left(\frac{1}{2}+\frac{1}{3}+....+\frac{1}{2015}\right)}=2015\)
