Răspuns :
c. C={x∈N | _4x+
3_ ∈N}
5x- 1
( 4x+ 3) : (5x- 1) ∈ IN
S₁: ( 4x+ 3) : (5x- 1) =1
( 4x+ 3) = (5x- 1)·1
4x + 3 = 5x- 1
3+ 1 =5x- 4x
4 = x
S₂: ( 4x+ 3) : (5x- 1) =2
( 4x+ 3) = (5x- 1)·2
4x + 3 = 10x- 2
3+ 2 =10x- 4x
5 = 6x
_5_ = x ∉ IN
6
Concluzie: C ={ 4}