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Cross Products of Side Vectors of Regular Hexagon

Let the vectors PQ⃗\vec{PQ}, QR⃗\vec{QR}, RS⃗\vec{RS}, ST⃗\vec{ST}, TU⃗\vec{TU} and UP⃗\vec{UP} represent the sides of a regular hexagon.

STATEMENT-1 : PQ⃗×(RS⃗+ST⃗)≠0⃗\vec{PQ} \times (\vec{RS} + \vec{ST}) \neq \vec{0}.
because
STATEMENT-2 : PQ⃗×RS⃗=0⃗\vec{PQ} \times \vec{RS} = \vec{0} and PQ⃗×ST⃗≠0⃗\vec{PQ} \times \vec{ST} \neq \vec{0}.

Options

A

Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1

B

Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1

C

Statement-1 is True, Statement-2 is False

Correct
D

Statement-1 is False, Statement-2 is True

Step-by-Step Solution

To determine the validity of the statements, let us analyze the geometry of the regular hexagon PQRSTUPQRSTU.

Analysis of Statement-2:
In a regular hexagon PQRSTUPQRSTU, the opposite sides are parallel:

  • Side PQPQ is opposite and parallel to side TSTS. Therefore, the vectors along these sides are related by:
    ST⃗=−PQ⃗\vec{ST} = -\vec{PQ}
    Since PQ⃗\vec{PQ} and ST⃗\vec{ST} are collinear (anti-parallel), their cross product is:
    PQ⃗×ST⃗=0⃗\vec{PQ} \times \vec{ST} = \vec{0}

  • Side RSRS is not parallel to side PQPQ; the angle between the vectors PQ⃗\vec{PQ} and RS⃗\vec{RS} is 120∘120^\circ. Thus:
    PQ⃗×RS⃗≠0⃗\vec{PQ} \times \vec{RS} \neq \vec{0}

Statement-2 asserts that PQ⃗×RS⃗=0⃗\vec{PQ} \times \vec{RS} = \vec{0} and PQ⃗×ST⃗≠0⃗\vec{PQ} \times \vec{ST} \neq \vec{0}, which is directly contrary to the geometric properties established above. Therefore, Statement-2 is False.


Analysis of Statement-1:
Using vector addition, we have:
RS⃗+ST⃗=RT⃗\vec{RS} + \vec{ST} = \vec{RT}
In △RST\triangle RST, the side lengths are equal (RS=STRS = ST) and the interior angle is ∠RST=120∘\angle RST = 120^\circ.
Therefore, △RST\triangle RST is an isosceles triangle with:
∠STR=∠SRT=180∘−120∘2=30∘\angle STR = \angle SRT = \frac{180^\circ - 120^\circ}{2} = 30^\circ

Since the line containing segment STST is parallel to the line containing segment PQPQ, the vector RT⃗\vec{RT} makes an angle of 30∘30^\circ (or 150∘150^\circ) with PQ⃗\vec{PQ}.

Because the angle between PQ⃗\vec{PQ} and RT⃗\vec{RT} is not 0∘0^\circ or 180∘180^\circ, the vectors PQ⃗\vec{PQ} and RT⃗\vec{RT} are not collinear:
PQ⃗×(RS⃗+ST⃗)=PQ⃗×RT⃗≠0⃗\vec{PQ} \times (\vec{RS} + \vec{ST}) = \vec{PQ} \times \vec{RT} \neq \vec{0}
Therefore, Statement-1 is True.


Conclusion:
Statement-1 is True and Statement-2 is False, which corresponds to option (C).