Resolution of a Vector Into Components

If the sum of two unit vectors is a unit vector, show that the magnitude of their difference is $\sqrt{3}$.

Find the magnitude of the vector $\overrightarrow{PQ}$ its scalar components and the component vectors along the co-ordinate axes, if $P$ and $Q$ have the co-ordinates: $P(1,4,-3), Q(2,-2,-1)$.

Find the magnitude of the vector $\overrightarrow{PQ}$ its scalar components and the component vectors along the co-ordinate axes, if $P$ and $Q$ have the co-ordinates: $P(-1,-2), Q(-5,-6)$.

Find the magnitude of the vector $\overrightarrow{PQ}$ its scalar components and the component vectors along the co-ordinate axes, if $P$ and $Q$ have the co-ordinates: $P(-1,3), Q(1,2)$.