Since we're given it must be that |a| divides 6 . This gives the possibilites:
1) |a| = 1
2) |a| = 2
3) |a| = 3
4) |a| = 6
You can test to see if our original equation is satisfied:
Suppose |a|= 2, then is still true that ? Well, and we know that |a| = 2 and so
therefore . So it still is true. If you're not convinced you can repeat this for the other cases.
Hope this helps.