cos(0,0,_,_,_,_).

cos(_,R,S,FN,XN,_):- 
	V = S*XN/FN,
        abs(V) < 0.00001,
        R = 0,
	!.

cos(X,R,S,FN,XN,N):-
      S1=S*(-1),
      N1=N+2,
      FN1=FN*(N+1)*(N+2),
      XN1=XN*X*X,
      cos(X,R1,S1,FN1,XN1,N1),
      R is R1+S*XN/FN.

cos(X,R):-cos(X,R1,-1,2,X*X,2),R is 1+R1.