Exercise 5

1. { x | 2x = 0} inside (R,+)
2. { x | 5x + 6 = 0 } inside (R,+)
3. { x | x^3 = 0 } inside (R,+)
4. { x | x^3 - 2x = 0 } inside (Z,+)
5. { x | 2x = [0] } inside (Z/6,+)
6. { x | x is prime} U {0} inside (Z,+)
7. { x | x is even} inside (Z,+)
8. { x | x is not invertible with respect to the multiplication} inside (Z/10,+)