\[\boxed{\mathbf{1066.ОК\ ГДЗ - домашка\ на}\ 5}\]
\[Дано:\ \]
\[\overrightarrow{a} = 3\overrightarrow{i} - 4\overrightarrow{j}.\]
\[Найти:\]
\[\left| \overrightarrow{a} \right| - ?\]
\[Решение.\]
\[\ \overrightarrow{a} = 3\overrightarrow{i} - 4\overrightarrow{j} \Longrightarrow \overrightarrow{a}\left\{ 3; - 4 \right):\]
\[\left| \overrightarrow{a} \right| = \sqrt{x^{2} + y^{2}} = \sqrt{9 + 16} =\]
\[= \sqrt{25} = 5.\]
\[Ответ:\left| \overrightarrow{a} \right| = 5.\]