Bonjour
a. (3x+ 1) (x - 5) = 0
3x + 1 = 0 ou x - 5 = 0
3x = - 1 x = 5
x = - 1/3
b. (3x + 7) (4x - 8) = 0
3x + 7 = 0 ou 4x - 8 = 0
3x = - 7 4x = 8
x = - 7/3 x = 8/7 = 2
c. 5 (9x - 3) (5x - 13) = 0
45x - 15 = 0 ou - 5x - 13 = 0
45x = 15 - 5x = 13
x = 15/45 = 1/3 x = - 13/5.