Răspuns :
n×4+23 <sau =43
n={0,1,2,3,4,5}
n=0
0×4+23=23=> 23 <43
n=1
1×4+23=27 => 27<43
n=2
2×4+23=31=> 31 <43
n=4
4×4+23=39=> 39 <43
n=5
5×4+23=43=> 43=43
n={0,1,2,3,4,5}
n=0
0×4+23=23=> 23 <43
n=1
1×4+23=27 => 27<43
n=2
2×4+23=31=> 31 <43
n=4
4×4+23=39=> 39 <43
n=5
5×4+23=43=> 43=43
n×4+23 ≤43 => n×4 ≤ 43-23 => n×4≤ 20 => n ≤ [tex] \frac{20}{4} [/tex] => n ≤ 5
=> n∈(-∞,5] ⊂ ℕ => n∈{0;1;2;3;4;5}
=> n∈(-∞,5] ⊂ ℕ => n∈{0;1;2;3;4;5}