Given is a modulus function |f(x)| that gives absolute value of the signed number written inside it.
For example |x|=2 means x = 2 or -2.
If the absolute value modulus function is zero ( i.e. |f(x)| = 0), then the expression inside the modulus function must be zero as well. It means f(x) = 0.
Now we have |a| = 0. So the possible solution of |a| = 0 must be {0}.
Hence, the answer is {0}.
