To simplify this expression, we first need to find a common denominator for both fractions.

First fraction: 1/a^2 + ab

Second fraction: 1/ab - a^2

The common denominator is (a^2)(ab), so we need to rewrite both fractions with this denominator:

(1/a^2 + ab) = (ab - a^3)/(a^2)(ab)

(1/ab - a^2) = (1 - a^3)/(a^2)(ab)

Now we can combine these two fractions:

(ab - a^3)/(a^2)(ab) - (1 - a^3)/(a^2)(ab)

= (ab - a^3 - 1 + a^3)/(a^2)(ab)

= (ab - 1)/(a^2)(ab)

Therefore, the simplified expression is (ab - 1)/(a^2)(ab).