bonsoir
A = - 10 x² + 8 x + 45 x - 36 - ( 81 x² + 90 x + 25 )
= - 10 x² + 53 x - 36 - 81 x² - 90 x - 25
= - 91 x² - 37 x - 61
B = 49 x² - 28 x + 4 - 18 x² - 12 x + 3 x + 2
= 31 x² - 37 x + 6
C = 100 x² - 1 - ( 20 x² - 32 x + 15 x - 24 )
= 100 x² - 1 - 20 x² + 32 x - 15 x + 24
= 80 x² + 17 x + 23