To multiply two numbers that are equidistant from another number using the difference of two squares identity, you would follow Option #1. The correct relationship is to set \( a \) as the middle number (midpoint) and \( x \) as the distance from the midpoint to either endpoint.
The equation would look like this: \((a - x)(a + x) = a^2 - x^2\).
Therefore, the correct option is:
Option #1: Use the equation \( x^2 - a^2 \), where \( a \) is the middle number (midpoint) and \( x \) is the distance from the midpoint to either endpoint.