Bonjour ,
1.
E = (5x-6) (x+4)
E = 5x * x + 5x * 4 - 6* x - 6 * 4
E = 5x^2 + 20x - 6x - 24
E = 5x^2 + 14x - 24 .
2.
- pour x =1/5 :
a.
E = (5*1/5-6) (1/5+4)
E = (5/5-6) (1/5+20/5)
E = (1-6) (21/5)
E = (-5) * 21/5
E = -105/5
E = -21 .
b.
E = 5* (1/5)^2 + 14 * 1/5 - 24
E = 5 * 1/25 + 14/5 - 24
E = 5/25 + 70/25 - 600/25
E = -525/25
E = -21 .