Résidu d'une expression en un point : residue

residue takes as argument an expression depending of a variable, this variable name and a complex a or an expression depending of a variable and the equality : variable_name=a. residue returns the residue of this exppression at the point a.
Input :

residue(cos(x)/x^3,x,0)

Or :

residue(cos(x)/x^3,x=0)

Output :

(-1)/2