Logarithme en base a
† Propriétés
† " x œ !
0+: y = log
ax ó x = a
y" x œ ! : log
aH a
xL = x
" x œ !
0+: a
loga x= x
† Propriétés
"x,yœ!0+
† loga 1=0 loga 1=loga a0=0
† loga a=1 loga a=loga a1=1
† logaHx.yL=loga x+logay on pose u=loga x et v=loga y on a alors x=au et y=av
logaHx.yL=logaHau.avL=loga au+v=u+v=loga x+loga y
† logaJ1xN= -loga x on pose u=loga x on a alors x=au
logaJ1xN=logaJa1uN=loga a-u= -u= -loga x
† logaJxyN=loga x-logay
logaJxyN=logaJx.1yN=loga x+loga 1y=loga x-logay
† log
ax
n= n . log
ax
on pose u=loga x on a alors x=au
loga xn=logaHauLn=loga an.u=n.u =n. loga x
† log
ax =
loglogb xb a on pose u=loga x on a alors x=au
logb x=logb au=u. logb a=loga x. logb a logb x=loga x. logb a
loga x= loglogb x
b a
2 proploga.nb