Question
Let $$P,\,Q,\,R$$ and $$S$$ be the points on the plane with position vectors $$ - 2\hat i - \hat j,\,4\hat i,\,3\hat i + 3\hat j$$ and $$ - 3\hat i + 2\hat j$$ respectively, The quadrilateral $$PQRS$$ must be a :
A.
parallelogram, which is neither a rhombus nor a rectangle
B.
square
C.
rectangle, but not a square
D.
rhombus, but not a square
Answer :
parallelogram, which is neither a rhombus nor a rectangle
Solution :
We have $$\overrightarrow {PQ} = 6\hat i + \hat j,\,\overrightarrow {QR} = - \hat i + 3\hat j,\,\overrightarrow {SR} = 6\hat i + \hat j,\,\overrightarrow {PS} = - \hat i + 3\hat j$$
$$\eqalign{
& \Rightarrow \overrightarrow {PQ} = \overrightarrow {SR} \,;\,\overrightarrow {QR} = \overrightarrow {PS} \,\,{\text{and }}\overrightarrow {PQ} .\overrightarrow {PS} \ne 0 \cr
& {\text{Also }}\left| {\overrightarrow {PQ} } \right| \ne \left| {\overrightarrow {QR} } \right| \cr} $$
$$ \Rightarrow PQRS$$ is a parallelogram but neither a rhombus nor a rectangle.