Question

Aflati a si b. A ={x apartine nr nat.|x apartine M5; x< 30} ; B={x apartine nr nat .| (x +5) divide pe 40}

Answer 1

x  ∈ M5;x < 30 => x ∈ { 5,10,15,20,25} pentru ca x < 30M5={5,10,15,20,25,30...}
A={ 5,10,15,20,25}
x+5|40 => x+5 ∈ D40=> x+5 ∈{ 1,2,4,5,8,10,20,40}
x+5=1=> x=1-5= -4 ∉ N
x+5=2=>x=2-5=-3 ∉ N 
x+5=4=>4-5=-1 ∉ N
x+5=5=>x=5-5=0 ∈ N
x+5=8=>x=8-5=3 ∈ N
x+5=10=>10-5=5 ∈ N
x+5=20=>20-5=15 ∈ N
x+5=40=>40-5=35 ∈ N
=> B={ 0 ,3,5,15,35}