Answer:
5(x - 5y)(x + 5y)
Step-by-step explanation:
Note that 5 is common to both terms. Thus,
5x² - 125y² = 5(x² - 25y²).
Also note that x² - 25y² is the difference of two squares and has factors (x - 5y) and (x + 5y).
In fully factored form, 5(x² - 25y²) is:
5(x - 5y)(x + 5y)
