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\(\left | p \right |=\sqrt{3^{2}+7^{2}}\)

\(\left | p \right |=\sqrt{9+49}\)

\(\left | p \right |=\sqrt{58}\)

\(\left| {\overrightarrow {PQ} } \right| = \sqrt {{5^2} + {4^2} + {{( - 2)}^2}} = \sqrt {45} = 3\sqrt 5 \,units\)

\(\left| {\overrightarrow {AB} } \right| = \left( {\begin{array}{*{20}{c}} 7\\ 9\\ { - 2} \end{array}} \right) - \left( {\begin{array}{*{20}{c}} 5\\ { - 1}\\ 2 \end{array}} \right) = \left( {\begin{array}{*{20}{c}} {7 - 5}\\ {9 - ( - 1)}\\ { - 2 - 2} \end{array}} \right) = \left( {\begin{array}{*{20}{c}} 2\\ {10}\\ { - 4} \end{array}} \right)\)

\(\left| {\overrightarrow {AB} } \right| = \sqrt {{2^2} + {{10}^2} + {{( - 4)}^2}} = \sqrt {120} = 2\sqrt {30} \,units\)