Explicație pas cu pas:
a) n+3|n+21
n+3|n+3
le scazi
n+3| 18
n+3 =D18 (in loc de egal sa pui apartine)
n+3={1,2,3,6,18} |-3
n={-2,-1,0,3,15}
n apartune N rezulta ca n={0,3,15}
b) n+3|2n+16
n+3|n+3 |*2
n+3| 2n+16
n+3|2n+6
le scazi
n+3| 10
n+3=D10
n+3={1,2,5,10} |-3
n={-2,-1,2,7}
n apartine N rezulta n={2,7}