Concept:
The radical plane of two spheres is obtained by subtracting their equations.
If the two spheres are
\[
S_1=0
\]
and
\[
S_2=0
\]
then the radical plane is
\[
S_1-S_2=0
\]
Step 1: Write the two sphere equations.
\[
S_1=x^2+y^2+z^2+4x-2y+2z+6=0
\]
\[
S_2=x^2+y^2+z^2+2x-4y-2z+6=0
\]
Step 2: Subtract \(S_2\) from \(S_1\).
\[
S_1-S_2=0
\]
\[
(x^2+y^2+z^2+4x-2y+2z+6)
-
(x^2+y^2+z^2+2x-4y-2z+6)=0
\]
Step 3: Cancel common terms.
The terms \(x^2,y^2,z^2\) and \(6\) cancel.
\[
4x-2x-2y+4y+2z+2z=0
\]
\[
2x+2y+4z=0
\]
Divide by \(2\):
\[
x+y+2z=0
\]
Step 4: Final answer.
\[
\boxed{x+y+2z=0}
\]