a) 6 (1 - x) = 6 - 6x
b) 3 (6x + 5 - 7x) = 18x + 15 - 21x = 15 - 3x
c) -5 (3a - 4x - 2a) = - 15a + 20x + 10a = -5a + 20x
d) 4 (y - 1)(y + 1) = 4 (y² - 1) = 4y² - 4
e) -x (-6 - 4x + 1) = 6x + 4x² - x = 4x² + 5x
f) (a + 2)(a - 2)(a - 1) = (a² - 4)(a - 1) = a³ - a² - 4a + 4
g) -(-z - 1)(-z - 1) = -(z² + z + z + 1) = -z² - 2z - 1
h) 9 (x + 5) - 2 (3x + 15) = 9x + 45 - 6x - 30 = 3x + 15
i) (5c + 8)(-5 - c) = -25c - 5c² - 40 - 8c = - 5c² - 33c - 40
j) (a + b)(-b + a) + (a - b)(a + b) = a² - b² + a² - b² = 2a² - 2b²
k) (¾ a + 0,4)(0,75a - ⅖) = (¾ a + ⅖)(¾ a - ⅖) = 9/16 a² - 4/25
l) (3,25b - 7)(8 - 2x) - 2 (13b + 7x) = 26x - 6,5xb - 56 + 14b - 26x - 14b = -6,5xb - 56
