Ta có : B = \(3+3^2+3^3+.....+3^{2002}\)
<=> B = \(3\left(3+3^2+1\right)\)+ .................... + \(3^{2000}\left(1+3+3^2\right)\)
<=> B = 3 . 13 + .................... + \(3^{2000}\). 13
<=> B = 13 . ( 3 + ....... + \(3^{2000}\) chia hết cho 13
=> B chia hết cho 13
( đpcm)