Aidez moi sur l'un des exercices

4) a)
A = 2x² - (3 + 7x) + (2x - 3x²) - 8 + 4x - 5
A = 2x² - 3 - 7x + 2x + 9x² - 8 + 4x - 5
A = 2x² + 9x² - 7x + 2x + 4x - 3 - 8 - 5
A = 11x² - x - 16

b)
A = 11x² - x - 16
A = 11 * 9 - 3 - 16
A = 99 - 19
A = 80

c)
B = 3/5 - 7/20 + 9/4 - 2
B = 3 x 4 / 5 x 4 - 7/20 + 9 x 5 / 4 x 5 - 2 x 20 / 1 x 20
B = 12/20 - 7/20 + 45/20 - 40/20
B = 57/20 - 47/20
B = 10/20
B = 10 x 1 / 10 x 2
B = 1/2

C = 9 - 3 x (8 + 2 x 3 - 4) - 7 + 2 x 3
C = 9 - 3 x (8 + 6 - 4) - 7 + 6
C = 9 - 3 x 9 - 7 + 6
C = 9 - 27 - 7 + 6
C = 15 - 34
C = - 19