first, let's focus in the equation we are given.
Squaring both sides of the equation, we get that
(a2+2+1/a2)=0
This means that we have a2+1/a2=−2
Now, let's focus on what we are trying to find.
Let's notice that
a3−1/a3=(a−1/a)(a2+1+1/a2)
Wait a minute! we already have all the terms needed. We know both values to solve the problem.
Since the first term is 0, we just have (0)(−1)=0
So 0 is our answer.
Thanks! :)