\(\left(\sqrt{2015}+\sqrt{2018}\right)^2=4033+2\cdot\sqrt{2015\cdot2018}\)
\(\left(\sqrt{2016}+\sqrt{2017}\right)^2=4033+2\cdot\sqrt{2016\cdot2017}\)
mà 2015*2018<2016*2017
nên (căn 2015+căn 2018)^2<(căn 2016+căn 2017)^2
=>căn 2015+căn 2018<căn 2016+căn 2017