Answer: 25x⁴ - 49
Step-by-step explanation:
(5x² - 7)(5x² + 7)
= 5x²(5x² + 7) - 7(5x² + 7)
= 25x⁴ + 35x² - 35x² - 49
= 25x⁴ + ( 0 ) - 49
= 25x⁴ - 49
