4=4
4²=16
4³=64
4⁴=...6
4⁵=...4
.........
4²⁰⁰⁰=...6
4²⁰⁰¹=....4
2001:2=1000 rest 1
A=4+16+..4+..6+..4+..6+...................+..4+..6+..4=....0+...+0......+0+....4=.....4
raspuns: ultima cifra a lui A=4
2) 3x+1≤6 /-1
3x≤6-1
3x≤5 / :3
x≤5/3
x≤1,(6)
x=0,1