Question: Equation of a plane (9)

Problem. Write the equation of the tangent planes to the sphere

x^2+  y^2 + z^2 -10*x +2*y +26*z -113=0

which are parallel to the lines

d1: x = -5+2*t, y = -3*t+1, z = -13+2*t

d2: x = -7+3*t, y = -1-2*t, z = 8.

This is my code

restart:

with(geom3d):

line(d1,[-5+2*t,-3*t+1,-13+2*t],t):

a:=ParallelVector(d1):

line(d2,[-7+3*t,-1-2*t,8],t):

b:=ParallelVector(d2):

with(linalg):

c:=crossprod(a,b):

sphere(S, x^2+  y^2 + z^2 -10*x +2*y +26*z -113=0,[x,y,z]):

point(T,coordinates(center(S))):

R:=radius(S):

Equation(plane(P,c[1]*x +c[2]*y +c[3]*z +m=0,[x,y,z])):

sol:=solve(distance(T,P)=R,{m});

for i from 1 to 2 do print( sort(Equation(plane(Q,eval(Equation(P),sol[i]),[x,y,z])))) end do;

Please comment to me, specialy the line 

Equation(plane(P,c[1]*x +c[2]*y +c[3]*z +m=0,[x,y,z])):

Thank you very much.