a) p² - 81 = (p - 9)(p + 9)

b) -1,21a² + b² = -(1,1a - b)(1,1a + b)

в) 49 - (2 - x)² = 49 - (4 - 4x + x²) = 49 - 4 + 4x - x² = -x² + 4x + 45 = -(x - 5)(x + 9)