format long
d=0;
x=[(cos(0.6)-0.6) (cos(0.7)-0.7) (cos(0.8)-0.8) (cos(0.9)-0.9)];
p=[0.6 0.7 0.8 0.9];
for i=1:3
  pp(i)=((d-x(i))*p(i+1)-(d-x(i+1))*p(i))/(x(i+1)-x(i));
  xx(i)=cos(pp(i))-pp(i);
end
for i=1:2
  ppp(i)=((d-xx(i))*pp(i+1)-(d-xx(i+1))*pp(i))/(xx(i+1)-xx(i));
  xxx(i)=cos(ppp(i))-ppp(i);
end
pppp=((d-xxx(1))*ppp(2)-(d-xxx(2))*ppp(1))/(xxx(2)-xxx(1))