Réponses

2014-02-17T13:49:40+01:00
D=(x-7) (5x+11) 
x*5x+x*11-7*5x-7*11
5x²+11x-35x-77
5x²-24x-77

x=7

on remplace tout simplement les x par 7

5x²-24x-77
5*(7)²-24*7-77
245-168-77
0
2014-02-17T13:55:38+01:00

1) D=(x-7) (5x+11)

= (x X 5x) + (x X 11) X (-7 X 5x) +(-7 X 11)

= 5x au carré + 11x -35x -77

=5x au carré - 24x -77

2) x=7

D= (7-7) (5X7+11)

=    (0) (35+11)

= 0 X 46

=0