Concept: Use cross product to find normal vector.
Step 1: Form vectors:
\[
\vec{AB}=(-2,2,-1),\quad \vec{AC}=(2,-1,-2)
\]
Step 2: Compute cross product:
\[
\vec{n}=\vec{AB}\times \vec{AC}
\]
Step 3: Determinant:
\[
\begin{vmatrix}
i & j & k
-2 & 2 & -1
2 & -1 & -2
\end{vmatrix}
\]
Step 4: Expand:
\[
i(-4-1) - j(4+2) + k(2-4)
= (-5,-6,-2)
\]
Step 5: Plane:
\[
-5(x-1)-6(y-2)-2(z-3)=0
\]
Step 6: Simplify:
\[
5x+6y+2z=13
\]