If you know Xi,Yi,Xj,Yj,Xk,Yk,can you calc the <ijk ( < mean jiao ).
if you can,write it to me.Thanks!

var
  xi,xj,xk,yi,yj,yk,j1,j2,jiao:real;
begin
  readln(xi,yi,xj,yj,xk,yk);
  if yi=yj then j1:=90 else j1:=arctan(abs(xj-xi)/abs(yj-yi))/pi*180;
  if xj>xi then j1:=360-j1;
  if yj>yi then j1:=180-j1;
  if j1<0then j1:=j1+360;
  if yk=yj then j2:=90 else
  j2:=arctan(abs(xj-xk)/abs(yj-yk))/pi*180;
  if xj>xk then j2:=360-j2;
  if yj>yk then j2:=180-j2;
  if j2<0then j2:=j2+360;
  jiao:=abs(j1-j2);
  if jiao>180then jiao:=360-jiao;
  {jiao is <IJK.}writeln(jiao:0:8)
end.