Răspuns
Explicație pas cu pas:
D₇₀={1, 2, 5, 7, 10, 14, 35, 70}
d) 2x+5=1 <=> 2x∉N
2x+5=2 <=> 2x∉N
2x+5=5 <=> 2x=0 => x=0
2x+5=7 <=> 2x=7-5 => x=1
2x+5=10 <=> 2x=10-5 <=> 2x=5 => x∉N
2x+5=14 <=> 2x=14-5 <=> 2x=9 => x∉N
2x+5=35 <=> 2x=35-5 <=> 2x=30 => x=30:2 => x=15.
2x+5=70 <=> 2x=70-5 <=> 2x=65 => x∉N
=> nr. sunt: 0, 1, 15.
