Bonjour, je ne comprend pas mon exercice de maths. (Niveau seconde) Merci de votre aide :)

Bonjour,
1) dom f=R-{-3}
2)4+5/(x+3)=4(x+3)/(x+3)+5/(x+3)=(4x+12+5)/(x+3)=(4x+17)/(x+3)
3)
  a) f(0)=(4*0+17)/(x+3)=17/3
      f(4/5)=(4*(4/5)+17)/(4/5+3)=(101/5)/(19/5)=101/19
   b) f(x)=0<=>(4x+17)/(x+3)=0<=>4x+17=0<=>x=-17/4
       f(x)=3 <=>(4x+17)/(x+3)=3<=>4x+17=3x+9<=>x=-8
   c)
f(x)<=0
(4x+17)/(x+3)<=0
                     -17/4        -3
4x+17  ----------0 +++++++++++++
x+3      ----------------------0+++++++++
(4x+17)/(x+3) + 0---------? +++++++++
donc -17/4<=x<-3

f(x)>4
   (4x+17)/(x+3)>4
<=> (4x+17-4x-12)/(x+3)>0
<=> 5/(x+3)>0
                     -3
x+3 ------------0  ++++
donc x>-3