\(\sqrt{2018^2+2018^2.2019^2+2019^2}=\sqrt{2018^2+\left(2019-1\right)^2.2019^2+2019^2}=\sqrt{2018^2+2019^4-2.2019.2019^2+2019^2+2019^2}=\sqrt{2019^4+2.2019^2-2.\left(2018+1\right).2019^2+2018^2}=\sqrt{2019^4+2.2019^2-2.2019.2019^2-2.2019^2+2018^2}=\sqrt{2019^4-2.2018.2019^2+2018^2}=\sqrt{\left(2019^2-2018\right)^2}=\left|2019^2-2018\right|=2019^2-2018\)Vì \(2019^2-2018\) là một số nguyên
Vậy \(\sqrt{2018^2+2018^2.2019^2+2019^2}\) là một số nguyên
TQ: \(^{\sqrt{a^2+a^2\left(a+1\right)^2+\left(a+1\right)^2}}=\left(a+1\right)^2-a.\)
Thật vậy ta có: \(a^2+a^2\left(a+1\right)^2+\left(a+1\right)^2=a^4+2a^3+3a^2+2a+1\)
\(\left(\left(a+1\right)^2-a\right)^2=\left(a^2+a+1\right)^2=a^4+2a^3+3a^2+2a+1\)