function f=exact1(M,N)
% You are solving exact type mdx+ndy=0 
      syms x y u u1 u2 u3 f1,M,N
      disp(' you are solving  M(x,y)dx+N(x,y)dy=0')
      disp(' where M = '); disp(M)
      disp(' and, where N = '); disp(N)      
      disp('check if equation is exact ........')
      u1=diff(M,y); disp('diff(M,y)='); disp(u1)
      u2=diff(N,x) ;disp('diff(N,x)=');disp(u2)
      u3=simplify(u2-u1) ;disp('u3=');disp(u3)
      if u3==0 
         disp('equation is exact if u3=0 ') 
         f1=int(M,x)
         disp(f1)        
         u2=simplify(-diff(f1,y)+N)
         disp(' solving for the arbitrary function of y is :')
         u=int(u2,'y')         
         disp(' The general  solution is F = constant =')
         f=simplify(f1+u)
     else
         disp(' u3 is not zero therfore ODE is not exact')  
     end      
 return