bonjour
1) 3 ( x + 5) ( 2 - x) = ( 3 x + 15) ( 2 - x ) = 6 x - 3 x² + 30 - 15 x
= - 3 x² - 9 x + 30
2) 8 x + 12 - 10 x² - 15 x = - 10 x² - 7 x + 12
3) 7 x² - ( x - 4) ( x - 5)
= 7 x² - ( x² - 5 x - 4 x + 20)
= 7 x² - x² + 5 x + 4 x - 20
= 6 x² + 9 x - 20