Bonsoir, help:( Mercii !:)

Bonsoir

a = 6 - 9 x - 6 x + 2
a = - 15 x + 8

b = 10 x - 8 - 8 x + 7
b = 2 x - 1

c = 6 x² - 8 + 15 x - 5 x² + 21 - 7 x + 9 x
c = x² + 17 x + 13