vous savez que
(a + b) (c + d) = a*c + a*d + b*c + b*d
on applique
A = (x+ 2) (x + 3) = x*x + x * 3 + 2 * x + 2 * 3
= x² + 3x + 2x + 6
= x² + 5x + 6
B = (x + 5) (2x + 4) = x * 2x + x * 4 + 5 * 2x + 5 * 4
= 2x² + 4x + 10x + 20
= 2x² + 14x + 20
et
C = (5x + 6) (3x + 4) = 5x * 3x + 5x * 4 + 6 * 3x + 6 * 4
= 15x² + 20x + 18x + 24
= 15x² + 38x + 24
