Răspuns:
b | a <=> 5x+35 | 7x+15 |*5
5x+35 | 5x+35 |*7
<=> 5x+35 | 5*(7x+15)
5x+35 | 7*(5x+35)
<=> 5x+35 | 35x+75
5x+35 | 35x+245
<=> 5x+35 | (35x+245) -(35x+75)
<=> 5x+35 | (245-75)
<=> 5x+35| 170 => 5x| 135 <=> x|27 => x ∈ D₂₇= {1;3;9;27}
a | b => 7x+15 | 5x+35 |*7
7x+15 | 7x+15 |*5
<=> 7x+15| 35x+245
7x+15| 35x+75
<=> 7x+15| diferenta- 170 => 7x|155 <=> x| 155/7 => x∉N
