4б) (5b² + 1)(1 - 5b²) = 1² - (5b²)² = 1 - 25b⁴
5a) x²y⁴ - 1 = (xy²)² - 1² = (xy² - 1)(xy² + 1)
5б) 81 - 64x²y² = 9² - (8xy)² = (9 - 8xy)(9 + 8xy)
4б) (5b² + 1)(1 - 5b²) = 1² - (5b²)² = 1 - 25b⁴
5a) x²y⁴ - 1 = (xy²)² - 1² = (xy² - 1)(xy² + 1)
5б) 81 - 64x²y² = 9² - (8xy)² = (9 - 8xy)(9 + 8xy)