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## 'Walls' printed from http://nrich.maths.org/

Let $P_1$ be a plane through the points $A(2,1,0), B(1,1,1)$ and
$C(1,7,3)$ and $P_2$ be a plane through the points $A$, $B$ and
$V(x,y,z)$. Find all the points $V(x,y,z)$ such that the two planes
are perpendicular.