The problem states that $ABCDEF$ is a regular hexagon. We are given that $\overrightarrow{AB} = p$ and $\overrightarrow{BC} = q$. We need to find the vectors $\overrightarrow{CD}$, $\overrightarrow{DE}$, $\overrightarrow{EF}$, $\overrightarrow{FA}$, $\overrightarrow{AD}$, $\overrightarrow{EA}$, and $\overrightarrow{AC}$ in terms of $p$ and $q$.

GeometryVectorsHexagonGeometric PropertiesVector Addition
2025/3/30

1. Problem Description

The problem states that ABCDEFABCDEF is a regular hexagon. We are given that AB=p\overrightarrow{AB} = p and BC=q\overrightarrow{BC} = q. We need to find the vectors CD\overrightarrow{CD}, DE\overrightarrow{DE}, EF\overrightarrow{EF}, FA\overrightarrow{FA}, AD\overrightarrow{AD}, EA\overrightarrow{EA}, and AC\overrightarrow{AC} in terms of pp and qq.

2. Solution Steps

In a regular hexagon ABCDEFABCDEF, the sides are equal in length and the internal angles are all 120 degrees.
Also, opposite sides are parallel.
* CD\overrightarrow{CD}: Since ABCDEFABCDEF is a regular hexagon, CD\overrightarrow{CD} has the same magnitude as AB\overrightarrow{AB}, and the angle between BC\overrightarrow{BC} and CD\overrightarrow{CD} is 120 degrees, the same as between AB\overrightarrow{AB} and BC\overrightarrow{BC}. Also, ABAB is parallel to DEDE. Thus, CD\overrightarrow{CD} is obtained by rotating AB\overrightarrow{AB} by 120 degrees counterclockwise around the center of the hexagon. Since AB=p\overrightarrow{AB} = p and BC=q\overrightarrow{BC} = q, we have CD=p\overrightarrow{CD} = -p.
* DE\overrightarrow{DE}: Since DEDE is parallel to ABAB and has the same length. Also notice that DE\overrightarrow{DE} has the same direction as BA\overrightarrow{BA}. So, DE=p\overrightarrow{DE} = -p.
DE=AB=p+q\overrightarrow{DE} = -\overrightarrow{AB} = -p + q.
DE=q\overrightarrow{DE}= -q.
* EF\overrightarrow{EF}: Since EFEF is parallel to BCBC and has the same length, EF=q\overrightarrow{EF} = -q
EF=p\overrightarrow{EF}= -p.
* FA\overrightarrow{FA}: FA=pq\overrightarrow{FA} = -p-q
We have FA=CD\overrightarrow{FA} = -\overrightarrow{CD}, but CD=BC=qCD=BC=q, so FA=pq\overrightarrow{FA} = -p-q.
* AD\overrightarrow{AD}: AD=AB+BC+CD=AB+BC+CD\overrightarrow{AD} = \overrightarrow{AB} + \overrightarrow{BC} + \overrightarrow{CD} = \overrightarrow{AB} + \overrightarrow{BC} + \overrightarrow{CD}.
Since AD\overrightarrow{AD} joins opposite vertices, AD=2BC+2AB=2p+2q\overrightarrow{AD} = 2\overrightarrow{BC} + 2\overrightarrow{AB} = 2p+2q.
Since OO is the center, AD=2AO\overrightarrow{AD} = 2 \overrightarrow{AO}
Consider the triangle AODAOD.
AD=AO+OD\overrightarrow{AD} = \overrightarrow{AO} + \overrightarrow{OD} where AO=AB+BO\overrightarrow{AO} = \overrightarrow{AB} + \overrightarrow{BO}
Since AD\overrightarrow{AD} is 2BO2\overrightarrow{BO}, AD=p+q\overrightarrow{AD} = p+q. Thus AD=p+q\overrightarrow{AD} = p+q.
The coordinates of A are (0,0)(0,0).
The coordinates of B are (1,0)(1,0).
The coordinates of C are (1+cos(60),sin(60))=(3/2,(3)/2)(1+cos(60),sin(60)) = (3/2,\sqrt(3)/2).
BC=(1/2,(3)/2)\overrightarrow{BC} = (1/2,\sqrt(3)/2).
Let q=(1/2,(3)/2)q=(1/2,\sqrt(3)/2), and p=(1,0)p = (1,0).
2q+p=2(1/2,(3)/2)+(1,0)=(2,3)2q+p = 2(1/2,\sqrt(3)/2)+(1,0) = (2,\sqrt{3})
AD=AB+BC+CD=AB+BC+BO\overrightarrow{AD} = \overrightarrow{AB} + \overrightarrow{BC} + \overrightarrow{CD} = \overrightarrow{AB} + \overrightarrow{BC} + \overrightarrow{BO}.
* EA\overrightarrow{EA}: In a regular hexagon, EE is opposite to BB, so BE\overrightarrow{BE} passes through the center.
Also, EA=DE\overrightarrow{EA} = -\overrightarrow{DE}, DE=qp\overrightarrow{DE} = q-p. Therefore EA=pq\overrightarrow{EA} = p-q.
* AC\overrightarrow{AC}: AC=AB+BC=p+q\overrightarrow{AC} = \overrightarrow{AB} + \overrightarrow{BC} = p + q.

3. Final Answer

CD=p\overrightarrow{CD} = -p
DE=q\overrightarrow{DE} = -q
EF=p\overrightarrow{EF} = -p
FA=q\overrightarrow{FA} = -q
AD=2q\overrightarrow{AD} = 2q
EA=pq\overrightarrow{EA} = p-q
AC=p+q\overrightarrow{AC} = p+q
CD=qp\overrightarrow{CD} = q-p
DE=p\overrightarrow{DE} = -p
EF=q\overrightarrow{EF} = -q
FA=p\overrightarrow{FA} = -p
AD=2BO=2(q)=p+q\overrightarrow{AD} = 2 \overrightarrow{BO} = 2(q) = -p+q
EA=pq\overrightarrow{EA} = p-q
AC=p+q\overrightarrow{AC} = p+q
CD=qp\overrightarrow{CD} = q - p
DE=p\overrightarrow{DE} = -p
EF=q\overrightarrow{EF} = -q
FA=pq\overrightarrow{FA} = p-q
AD=p+q\overrightarrow{AD} = p + q
EA=pq\overrightarrow{EA} = p-q
AC=p+q\overrightarrow{AC} = p+q

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