a) Ta có: \(2019\equiv3\left(mod9\right)\)
=> \(A=2019^{2018}\equiv3^{2018}\equiv3^{2.1009}\equiv9^{1009}\equiv0\left(mod9\right)\)
=> A chia 9 dư 0
b) Ta có: \(2020\equiv10\left(mod15\right)\)
=> \(B=2020^{2019}\equiv10^{2019}\equiv10\left(mod15\right)\)
=> B chia 15 dư 10.