Bonjour,
A = x (12x - 7y)
A = x * 12x + x * (-7y)
A = 12x² - 7xy
B = 7x²(y - 2)
B = 7x² * y + 7x² * (-2)
B = 7x²y - 14x²
C = 9xy(x + 5)
C = 9xy * x + 9xy * 5
C = 9x²y + 45xy
D = 7t(t² - 2t)
D = 7t * t² + 7t * (-2t)
D = 7t³ - 14t²
E = 5(x + 3x)
E = 5 * x + 5 * 3x
E = 5x + 15x
E = 20x
F = 8xy(9x + 7y)
F = 8xy * 9x + 8xy * 7y
F = 72x²y + 56xy²
G = 10x(x² + 4)
G = 10x * x² + 10x * 4
G = 10x³ + 40x