Répondre :
f(x)=3-cos(x)/(x-3)
-1 < cos(x) < 1
-1/(x-3) < cos(x) < 1/(x-3) si x>3
3-1/(x-3) < f(x) < 3+1/(x-3)
donc lim(f(x)=+inf)=3
de même si <3 on a -1/(3-x) < cos(x) < 1/(3-x)
donc 3-1/(3-x) < f(x) < 3+1/(3-x)
donc lim(f(x),-inf)=3
-1 < cos(x) < 1
-1/(x-3) < cos(x) < 1/(x-3) si x>3
3-1/(x-3) < f(x) < 3+1/(x-3)
donc lim(f(x)=+inf)=3
de même si <3 on a -1/(3-x) < cos(x) < 1/(3-x)
donc 3-1/(3-x) < f(x) < 3+1/(3-x)
donc lim(f(x),-inf)=3