Répondre :
[sin(x+h)-sin(x)]/h = (2sin(h/2.)cos(2x+h)/2)/h
lim(2sin(h/2.)cos(2x+h)/2)/h = lim 2sin(h/2)/2.(h/2) . limcos(2x+h)/2)
= 1.cos(2x/2) = cosx
donc sin'x = cosx
lim(2sin(h/2.)cos(2x+h)/2)/h = lim 2sin(h/2)/2.(h/2) . limcos(2x+h)/2)
= 1.cos(2x/2) = cosx
donc sin'x = cosx