Vectors

Add, subtract, and use vectors in geometry for GCSE Maths. Represent vectors as column vectors and express paths.

Vectors have both magnitude (size) and direction. In GCSE Maths, vectors are used to describe translations and prove geometric properties.

Core Concepts

Notation

  • Column vector: (32)\binom{3}{-2} (3 right, 2 down).
  • Named vector: AB\vec{AB} or a\mathbf{a}.

Operations

Addition: (23)+(14)=(31)\binom{2}{3} + \binom{1}{-4} = \binom{3}{-1}

Subtraction: (52)(31)=(21)\binom{5}{2} - \binom{3}{1} = \binom{2}{1}

Scalar multiplication: 3(21)=(63)3\binom{2}{-1} = \binom{6}{-3}

Reverse Direction

BA=AB\vec{BA} = -\vec{AB}

Expressing Paths

To go from A to C via B: AC=AB+BC\vec{AC} = \vec{AB} + \vec{BC}.

Parallel Vectors

If PQ=kRS\vec{PQ} = k\vec{RS} for some scalar kk, the vectors are parallel.

Midpoints

If M is the midpoint of AB: OM=OA+12AB\vec{OM} = \vec{OA} + \frac{1}{2}\vec{AB}.

Worked Example: Example 1

Problem

OA=a\vec{OA} = \mathbf{a}, OB=b\vec{OB} = \mathbf{b}. Find AB\vec{AB}.

AB=AO+OB=a+b=ba\vec{AB} = \vec{AO} + \vec{OB} = -\mathbf{a} + \mathbf{b} = \mathbf{b} - \mathbf{a}

Solution

Worked Example: Example 2

Problem

M is the midpoint of AB. OM=12(a+b)\vec{OM} = \frac{1}{2}(\mathbf{a} + \mathbf{b}).

Solution

Practice Problems

    1. OA=(34)\vec{OA} = \binom{3}{4}, OB=(71)\vec{OB} = \binom{7}{1}. Find AB\vec{AB}.
    1. Show that (64)\binom{6}{-4} is parallel to (32)\binom{3}{-2}.
    1. M is the midpoint of PQ. OP=2a\vec{OP} = 2\mathbf{a}, OQ=4b\vec{OQ} = 4\mathbf{b}. Find OM\vec{OM}.

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Key Takeaways

  • Vectors have magnitude and direction.

  • AB=OBOA=ba\vec{AB} = \vec{OB} - \vec{OA} = \mathbf{b} - \mathbf{a}.

  • Parallel: one is a scalar multiple of the other.

  • Midpoint: OM=12(a+b)\vec{OM} = \frac{1}{2}(\mathbf{a} + \mathbf{b}).

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