Răspuns:
10. Multipli de 2: 1,2,4,6,8
Multipli de 3: 1,3,6,9
Multipli de 4: 1,4,8
Multipli de 5: 1,5
11.a) Multipli de 9: 1,9,18,27
b) Multipli de 8: 1,8,16,24
c) Multipli de 7: 1,7,14,21,28
d) Multipli de 6: 1,6,12,18,24,30
12. a) Multipli de 20: 1, 20, 40, 60, 80
b) Multipli de 25: 1, 25, 50, 75
c) Multipli de 30: 1, 30, 60, 90
d) Multipli de 27: 1, 27, 54, 81
13. a) Multipli de 5: 1,5,10,15, 20, 25, 30
b) Multipli de 7: 1, 7, 14, 21, 28, 35, 42
c) Multipli de 8: 1, 8, 16, 24, 32, 40, 48
d) Multipli de 9: 1, 9, 18, 27, 36, 45, 54
e) Multipli de 10: 1, 10, 20, 30, 40, 50, 60
f) Multipli de 12: 1, 12, 24, 36, 48, 60, 72
g) Multipli de 14: 1, 14, 28, 42, 56, 70, 84
h) Multipli de 15: 1, 15, 30, 45, 60, 75, 90
14. a) fals
b) adevarat
c) fals
d) fals
17. a+(a+1)+(a+2)=3a+3=> 3(a+1)=> suma a trei nr consecutive se divide cu 3
19. a)[tex]2^{n}[/tex] x [tex]5^{n+1}[/tex]- [tex]2^{n+1}[/tex] x [tex]5^{n}[/tex]=
[tex]2^{n}[/tex] x [tex]5^{n}[/tex] x 5 - [tex]2^{n}[/tex] x 2 x [tex]5^{n}[/tex] =
[tex]10^{n}[/tex] x 5- [tex]10^{n}[/tex] x 2=
[tex]10^{n}[/tex] x (5-2)=
[tex]10^{n}[/tex] x 3 =>nr este multiplu de 3
b) [tex]2^{n}[/tex] x [tex]3^{n+1}[/tex] + [tex]2^{n+2}[/tex] x [tex]3^{n}[/tex]=
[tex]2^{n}[/tex] x [tex]3^{n}[/tex] x 3 + [tex]2^{n}[/tex] x 4 x [tex]3^{n}[/tex]=
[tex]6^{n}[/tex] x 3+ [tex]6^{n}[/tex] x 4=
[tex]6^{n}[/tex] x (3+4)=
[tex]6^{n}[/tex] x 7=> nr este multiplu de 7
