📘 Remember
Vectors carry both magnitude and direction. Work with horizontal and vertical components separately, and keep signs consistent.
🎯 Learning Objectives
- express edges and diagonals using vectors;
- use parallelogram and triangle properties;
- simplify vector routes;
- prove lines are parallel or points are collinear.
Introduction
This lesson develops Vector Properties of Plane Shapes from meaning and patterns before moving to calculations. Look for what the quantities, shapes or symbols represent, then connect that idea to the method.
Key Notes
Read the definitions and key facts below carefully. Each rule is most useful when you can explain why it fits the situation, not simply recall it.
Vectors in a Parallelogram
Proving Parallelism
If one vector is a scalar multiple of another, the lines are parallel.
🧭 Interactive Diagram: Parallelogram Vector Properties
Drag the orange vertex. Opposite sides remain equal and parallel, and the diagonal is the sum of two adjacent side vectors.
Try it: drag vertex C and observe how AB = DC and AD = BC remain true.
AB and DC are equal; AD and BC are equal; AC = AB + BC.
🧠 Let’s Think Together
Before calculating, identify the information given, the result required and the mathematical relationship that connects them. Predict whether the answer should be larger, smaller or unchanged, then use that prediction to check the result.
Worked Examples
Reason through the method
- Identify the known information and what must be found.
- Choose the definition, property or formula that connects them.
- Substitute carefully and show each step.
- Check the notation, units and whether the result is sensible.
Practice Questions
- In parallelogram ABCD, AB⃗=a and AD⃗=b. Express AC⃗.
- Express DB⃗ in terms of a and b.
- Explain why vectors (4,6) and (−2,−3) are parallel.
- What vector condition shows three points are collinear?
✅ Check Your Work
Show answers and working
- AC⃗=a+b.
- DB⃗=DA⃗+AB⃗=−b+a=a−b.
- (4,6)=−2(−2,−3), so they are scalar multiples.
- Two direction vectors along the same line are scalar multiples.
⚠️ Common Mistakes
Do not confuse a point with its position vector. For AB, always calculate B − A, not A − B.
⭐ Exam Tips
Sketch arrows, label directions clearly, show component working and check whether the final direction agrees with the diagram.
🌍 Did You Know?
Vectors are used in navigation, animation, engineering, robotics, weather modelling and computer games.
Common Mistakes
- Choosing a rule before identifying what the question describes.
- Skipping working or changing notation part-way through a solution.
- Accepting an answer without checking its size, sign or units.
Exam Focus
Show the mathematical relationship you are using, keep notation consistent and give a clear final answer. Use a quick estimate, diagram or inverse operation to check that the result is reasonable.
Summary
- Understand the meaning of each idea before selecting a method.
- Use definitions, properties and notation consistently.
- Show working and check that the final result is sensible.