bonjour,
a) (x+5/2)²-9/4
[x+b/2a)²-Δ/4a = [x+5/2]²-[(-5)²-4(1*4)]/4*1
(x+5/2)²-(25-16)/4 =
(x+5/2)²-9/4
c) on facto (x+5/2)²-9/4
(x+5/2-3/2)(x+5/2+3/2) =
(x+2/2)(x+8/2)=
(x+1)(x+4)
4) résoudre f(x) = 4
x²+5x+4 = 4
x²+5x+4-4 =0
x²+5x = 0
x(x+5) = 0
x =(-5; 0)
e) résoudre f(x) = 0
(x+1)(x+4)
x= (-1;-4)