Bonjour
1)
A = xy + 4
A = 3 * 2 + 4
A = 6 + 4
A = 10
2)
B = x (x + 2) - 4x
B = 2 (2 + 2) - 4 * 2
B = 2 * 4 - 8
B = 8 - 8
B = 0
C = 5x² - 3x + 7
C = 5 * (- 4)² - 3 * (- 4) + 7
C = 5 * 16 + 12 + 7
C = 80 + 19
C = 99
D = a/b
D = 2/21 : 5/- 7
D = - 2/21 x - 7/5
D = 14/105
D = (7 x 2) / (7 x 15)
D = 2/15.