Final answer:
The best endpoint for using polynomial identities to convert differences of numerical squares into products is (a² - b²).
Step-by-step explanation:
To convert differences of numerical squares into products using polynomial identities, we need to use the difference of squares formula. The formula is (a² - b²) = (a + b)(a - b). Comparing this formula to the given options, we can see that option d. (a² - b²) is best suited for using polynomial identities.