Please write a code for me about following problem.

Let A(0,1,2) be a point and two lines

d1: x/2 = (y-1)/1 = (z+1)/(-1)

d2: x = 1 + t, y = -1 + 2t, 2 + t.

Find the coordinates of the 

Write the equation for the plane P contains the straight line 

d: x = 2 + t, y = t, z = 2 + 2t,

so that, the distance  

Problem: Write the equation of the straight line (d) through the point A(1,-2,3), cut the straight line 

Delta: x = 3*t+1, y = t, z = t-1 and parallel to the plane (P): x + 2*y + 3*z + 4 = 0.

We know that, if the straight line (d) through the point A and parallel to the plane (P), then (d) lies on a plane (Q), which (Q) through the point A and parallel to the plane (P).

Write the equation of a pane (P) which passes through the point E(2,1,0) and F(1,2,1) such that distance from the point A(1,-2,-1) to the plane (P) twice distance from the point B(2,4,3) to the plane (P).

My main idea is based on, if the line (d) passes through...

Please write for me a proceduce in order to write the eqution of the common perpendicular to the two skewline 

d: x = 3*t - 7, y = -2*t +4, z = 3*t + 4 and

l: x = m + 1, y = 2m - 9, z = -m - 12.

I did:

with(geom3d);

line(d,[3*t-7,-2*t+4,3*t+4],t);

line(l,[m + 1,2*m - 9, - m - 12],m);

u:=ParallelVector(d);

v:=ParallelVector(l);

with(linalg);

w:=crossprod(u,v);

a:=crossprod(u,w);