Bonjour,
A = (6x + 3)(x+10)
A = 6x * x + 6x * 10 + 3 * x + 3 * 10
A = 6x² + 60x + 3x + 30
A = 6x² + 63x + 30
B = (9x-4) (7x+1)
B = 9x * 7x + 9x * 1 - 4 * 7x - 4 * 1
B = 63x² + 9x - 28x - 4
B = 63x² - 19x - 4
C = (x+5)²
C = (x+5) (x+5)
C = x *x + x * 5 + 5 * x + 5 * 5
C = x² + 5x + 5x + 25
C = x² + 10x + 25
