• # question_answer The lengths of the diagonals of a parallelogram constructed on the vectors $\vec{p}=2\vec{a}+\vec{b}$ & $\vec{q}=\vec{a}-2\vec{b}$ where $\vec{a}$ & $\vec{b}$ are unit vectors forming an angle of $60{}^\circ$ are: A) 3 & 4 B) $\sqrt{7}$&$\sqrt{13}$ C) $\sqrt{5}$ &$\sqrt{11}$ D) none of these

Solution :

$|{{\vec{d}}_{1}}|\,\,=\,\,|\vec{p}+\vec{q}|\,\,;\,\,|{{\vec{d}}_{2}}|\,\,=\,\,|\vec{p}-\vec{q}|$

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