Answer

(d) : Equation of any plane parallel to the plane
$x-2 y+2 z+4=0 \text { is } x-2 y+2 z+\lambda=0 \text {. }$
Its distance from the point $(1,2,3)$ is 1 unit.
$\begin{aligned}
& \therefore \frac{|1-2(2)+2(3)+\lambda|}{\sqrt{1^2+(-2)^2+(2)^2}}=1 \Rightarrow \frac{|1-4+6+\lambda|}{3} \\
& \Rightarrow|3+\lambda|=3 \\
& \Rightarrow 3+\lambda= \pm 3 \Rightarrow \lambda=0,-6
\end{aligned}$
$\therefore$ Equations of planes are
$x-2 y+2 z=0 \text { and } x-2 y+2 z-6=0$

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