a=\(\frac{-7}{2018^{2019}}+\frac{-15}{2018^{2018}}=\frac{-7-15.2018}{2018^{2019}}\)
b=\(\frac{-15}{2018^{2019}}+\frac{-7}{2018^{2018}}=\frac{-15-7.2018}{2018^{2019}}\)
Ta có: -7-15.2018 < -15-7.2018
\(\Rightarrow\frac{-7-15.2018}{2018^{2019}}< \frac{-15-7.2018}{2018^{2019}}\)
\(\Rightarrow a< b\)