Answer: a) 125x³ - 64y³
Step-by-step explanation:
(25x² + 20xy + 16y²)(5x - 4y)
= (5x - 4y)(25x² + 20xy + 16y²)
= 5x(25x² + 20xy + 16y²) -4y(25x² + 20xy + 16y²)
= 125x³ + 100x²y +80xy²
+ -100x²y -80xy² - 64y³
= 125x³ -64y³
