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Vectors

邊玩邊學

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課程筆記

Introduction to Column Vectors

  • A column vector describes a translation: e.g. \begin{pmatrix}6\\3\end{pmatrix} means 6 right, 3 up.
  • Add/subtract vectors component-wise: top numbers together, bottom numbers together.
  • Multiply a vector by a scalar (a number) by multiplying each component.
  • Follow order of operations when combining scalar multiplication and addition.
  • Example: 2\begin{pmatrix}5\\2\end{pmatrix}+5\begin{pmatrix}3\\-1\end{pmatrix}=\begin{pmatrix}10\\4\end{pmatrix}+\begin{pmatrix}15\\-5\end{pmatrix}=\begin{pmatrix}25\\-1\end{pmatrix}.

Column vector components

Column vector components

Representing Vectors as Diagrams

  • A vector has magnitude (size) and direction; shown by an arrow.
  • Vectors are written in bold (or underlined by hand), e.g. \mathbf{a} or \underline{a}.
  • \overrightarrow{AB} goes from A to B; \overrightarrow{BA} is opposite direction.
  • To draw \begin{pmatrix}3\\4\end{pmatrix}, start at a point, move 3 right, 4 up, draw arrow.
  • Multiplying by a positive scalar changes length but not direction; negative scalar reverses direction.
  • To add vectors diagrammatically, place them tip-to-tail; the resultant goes from start to end.

Drawing vectors a, b and c on a grid

Drawing vectors a, b and c on a grid

Magnitude of a Vector

  • The magnitude (modulus) of a vector is its length, always positive.
  • For \mathbf{a}=\begin{pmatrix}x\\y\end{pmatrix}, |\mathbf{a}|=\√{x2+y2} (Pythagoras).
  • Magnitude is independent of direction: |\overrightarrow{AB}|=|\overrightarrow{BA}|.
  • If a vector is multiplied by scalar k, its magnitude is multiplied by |k|.

The magnitude of a vector as the hypotenuse PQ

The magnitude of a vector as the hypotenuse PQ

Position & Displacement Vectors

  • A position vector locates a point relative to the origin O: \overrightarrow{OA}=\mathbf{a}.
  • Coordinates equal components: point (3,-2) has position vector \begin{pmatrix}3\\-2\end{pmatrix}.
  • A displacement vector goes from one point to another: \overrightarrow{AB}=\mathbf{b}-\mathbf{a}.
  • Use \overrightarrow{AB}=-\mathbf{a}+\mathbf{b} to find displacement from position vectors.

Position and displacement vectors in triangle OAB

Position and displacement vectors in triangle OAB

Finding Vector Paths

  • A vector path is a sequence of vectors from start to end.
  • In a grid of parallelograms, horizontal moves are multiples of one vector, diagonal moves of another.
  • Count steps in each direction to express a vector in terms of given vectors.
  • Negative signs indicate opposite direction.

A grid of parallelograms for vector paths

A grid of parallelograms for vector paths

Problem Solving with Vectors

  • Two vectors are parallel if one is a scalar multiple of the other.
  • To prove three points are collinear, show two vectors between them are parallel and share a common point.
  • Ratios along a line: if AX:XB=3:5, then \overrightarrow{AX}=\frac{3}{8}\overrightarrow{AB}.
  • Use vector algebra to find unknown points or prove geometric properties.

Trapezium OABC

Trapezium OABC

投影片

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練習題

免費預覽——52 題中的 8 題。註冊即可查看全部。
  1. 1.What is the column vector representing a translation of 3 units to the right and 4 units down?

    Easy
    • A\begin{pmatrix}3\\-4\end{pmatrix}
    • B\begin{pmatrix}-3\\4\end{pmatrix}
    • C\begin{pmatrix}3\\4\end{pmatrix}
    • D\begin{pmatrix}-3\\-4\end{pmatrix}
  2. 2.Given \mathbf{a} = \begin{pmatrix}5\\2\end{pmatrix} and \mathbf{b} = \begin{pmatrix}3\\-1\end{pmatrix}, find \mathbf{a} + \mathbf{b}.

    Easy
    • A\begin{pmatrix}8\\1\end{pmatrix}
    • B\begin{pmatrix}8\\3\end{pmatrix}
    • C\begin{pmatrix}2\\1\end{pmatrix}
    • D\begin{pmatrix}2\\3\end{pmatrix}
  3. 3.Given \mathbf{a} = \begin{pmatrix}4\\-2\end{pmatrix}, what is 2\mathbf{a}?

    Easy
    • A\begin{pmatrix}8\\-4\end{pmatrix}
    • B\begin{pmatrix}6\\0\end{pmatrix}
    • C\begin{pmatrix}8\\4\end{pmatrix}
    • D\begin{pmatrix}2\\-1\end{pmatrix}
  4. 4.Find the magnitude of the vector \begin{pmatrix}3\\4\end{pmatrix}.

    Easy
    • A5
    • B7
    • C12
    • D25
  5. 5.The displacement vector from A to B is \overrightarrow{AB} = \mathbf{b} - \mathbf{a}. If \mathbf{a} = \begin{pmatrix}2\\5\end{pmatrix} and \mathbf{b} = \begin{pmatrix}7\\1\end{pmatrix}, what is \overrightarrow{AB}?

    Easy
    • A\begin{pmatrix}5\\-4\end{pmatrix}
    • B\begin{pmatrix}5\\4\end{pmatrix}
    • C\begin{pmatrix}-5\\4\end{pmatrix}
    • D\begin{pmatrix}9\\6\end{pmatrix}
  6. 6.Given \mathbf{p} = \begin{pmatrix}4\\5\end{pmatrix} and \mathbf{q} = \begin{pmatrix}-2\\7\end{pmatrix}, find 2\mathbf{p} + \mathbf{q}.

    Easy
    • A\begin{pmatrix}6\\17\end{pmatrix}
    • B\begin{pmatrix}6\\-3\end{pmatrix}
    • C\begin{pmatrix}2\\12\end{pmatrix}
    • D\begin{pmatrix}10\\12\end{pmatrix}
  7. 7.Given \mathbf{a} = \begin{pmatrix}-3\\2\end{pmatrix}, find |\mathbf{a}|.

    Easy
    • A\√{13}
    • B\√{5}
    • C13
    • D5
  8. 8.Point A is (6,4) and point B is (2,7). Write \overrightarrow{AB} as a column vector.

    Easy
    • A\begin{pmatrix}-4\\3\end{pmatrix}
    • B\begin{pmatrix}4\\-3\end{pmatrix}
    • C\begin{pmatrix}-4\\-3\end{pmatrix}
    • D\begin{pmatrix}4\\3\end{pmatrix}

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