Final answer:
The expression (2/z) (7/a⁶) cannot be simplified when z=0 because dividing by zero is undefined in mathematics.
Step-by-step explanation:
The question asks what is the fraction (2/z) (7/a⁶) expressed in lowest terms when z=0. However, when trying to evaluate this expression, we encounter an issue. The value of 'z' is in the denominator, so if z=0, we cannot divide by zero as it is undefined in mathematics. Therefore, the expression (2/0) (7/a⁶) is undefined and cannot be simplified or expressed in lowest terms. Dividing by zero is not allowed, and any expression that involves division by zero does not have a value.