a.
D15 = {1,3,5,15}
x+1 ∈ {1,3,5,15} ⇒ x∈ {0,2,4,14}
b.
D26= {1,2,13,26}
2x+1 | 26
2x+1= {1,2,13,26} scadem -1
2x= {0,1,12,25} impartim prin 2
x= {0,6}
D32= {1,2,4,8,16,32}
2x+4 | 32
2x+4= {1,2,4,8,16,32} scadem -4
2x = {0,4,12,28} impartim la 2
x= {0,2,6,14}
D70 = {1,2,5,7,10,14,35,70}
2x+5 = {1,2,5,7,10,14,35,70} scadem -5
2x= { 0,2,5,9,30,65} impartim la 2
x= { 0,1,15}
D45={1,3,5,9,15,45}
3x-3={1,3,5,9,15,45}\-3
3x={-2,0,2,6,12,42}\:3
x={0,2,4,14}