1: Find the distance between the points $P=(1,2,3)$ and $Q=(4,5,6)$.
Solution: We can use the distance formula in three dimensions:
$$d(P,Q) = \sqrt{(x_2-x_1)^2 + (y_2-y_1)^2 + (z_2-z_1)^2}$$
Plugging in the coordinates of $P$ and $Q$, we get:
$$d(P,Q) =
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