With(geom3d), equation of  a line has the form a parametric equation. How  i can get canonical equation of a line? Please help me?

I can't write a program to solve the following problem:

The first two terms of a sequence are a1 = 1, a2 = 1/sqrt(3). For n >=1, a(n+2) = (an + a(n+1))/(1-an*a(n+1)). What is a2012?

I want to find all integral solution of the equation x =

Pi/9+2*k*Pi/3, where k is integral numbeer and 1 <= x <=2^Pi. 

This is my code. 

restart; solve([Pi/9+2*k*Pi/3 >=1,Pi/9+2*k*Pi/3 <=2^Pi],k);

> evalf(%);

 > f:=k->Pi/9+2*k*Pi/3;

 > seq(f(k),k = 1..4);

Please help me another way. Thank you.

Write the equation of the sphere passing through the point B(-1,-1,0) and tangent to the line x = t + 1, y = 2*t + 1, z = -t + 2 at the point A(1, 3, 2) so that its radius obtain minimum value.

This is my code.

> restart:with(geom3d):

point(B,-1,-1,0):

point(A,1,3,2):

a:=[t+1,2*t+3,-t+2]:

line(Delta,a,t):

dsegment(AB,[A,B]):

Problem 1. Write the equation of the sphere passing through three points A(2, 3, -2), B(-2, 3, 4), C(0, -1, 2) and  tangent to the plane (P): x+5*y+z-33=0.

This is my code

> restart:with(geom3d):

point(A,2,3,-2):

point(B,-2,3,4):

point(C,0,-1,2):

plane(P,x+5*y+z-33=0,[x,y,z]):

point(T,x,y,z):