1.5a+4b-20=0
b=numar natural⇒ 5a+4b-20=0⇒a∈{ 0,1,2,3,4}⇒b∈{1,2,3} sau a=2 pentru ca: 2x5a+3x4b=10+12=22 ⇒ a-numar par
2.D12={1,2,3,4,6,12}
D18={1 ; 2 ; 3 ; 6 ; 9 ; 18}
D={1;2;3;6}
3.x=?
(x-1)= x+1=8 x=7
4..M={14;28;56}
5.210
8.Orice numar care are suma cifrelor divizibila cu 3 se imparte la 3.(cred)