Final answer:
To factor the expression completely, we can use the difference of squares formula and then further factor if necessary.
Step-by-step explanation:
To factor the expression 81x⁴ - 625y⁴ completely, we can use the difference of squares formula. The formula states that a² - b² can be factored as (a + b)(a - b). In this case, 81x⁴ is the square of 9x² and 625y⁴ is the square of 25y². Therefore, we have:
81x⁴ - 625y⁴ = (9x² + 25y²)(9x² - 25y²)
To simplify the answer, we can further factor the difference of squares 9x² - 25y² as (3x + 5y)(3x - 5y), which gives us the completely factored expression:
81x⁴ - 625y⁴ = (9x² + 25y²)(3x + 5y)(3x - 5y)