1. Tính ( bằng 2 cách ) :
a ) S= 1+2+3+...+2018
b ) S = 1+3+5+.....+2019
2. Tính ( bằng 2 cách )
a ) S= 2+22 + 23 + 24 + ....+ 22018
b ) S = 1+4+7+10+.....+2020
c) B= 1+6+11+16+....+2021
d ) A = 3+32 + 33 +....+32005
e) E = \(\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+.....+\dfrac{1}{3^{2005}}\)