Lets Find It Out..
First we'll find the equation of ALL planes parallel to the original one.
As a model consider this lesson:
Equation of a plane parallel to other
The normal vector is:
→n=<1,2−2>
The equation of the plane parallel to the original one passing through P(x0,y0,z0)is:
→n⋅< x−x0,y−y0,z−z0>=0
<1,2,−2>⋅<x−x0,y−y0,z−z0>=0
x−x0+2y−2y0−2z+2z0=0
x+2y−2z−x0−2y0+2z0=0
Or
x+2y−2z+d=0 [1]
where a=1, b=2, c=−2 and d=−x0−2y0+2z0
Now we'll find planes that obey the previous formula and at a distance of 2 units from a point in the original plane. (We should expect 2 results, one for each half-space delimited by the original plane.)
As a model consider this lesson:
Distance between 2 parallel planes
In the original plane let's choose a point.
For instance, when x=0 and y=0:
x+2y−2z=1 => 0+2⋅0−2z=1 => z=−12
→P1(0,0,−12)
In the formula of the distance between a point and a plane (not any plane but a plane parallel to the original one, equation [1] ), keeping D=2, and d as d itself, we get:
D=|ax1+by1+cz1+d|√a2+b2+c2
