CSEC ADDITIONAL MATHEMATICS · SECTION 2 · LESSON B3

Vectors in Two Dimensions: i, j Notation, Magnitude and Direction

Scalars and vectors, column and i, j notation, equal vectors, addition, subtraction and scalar multiples, unit vectors, position and displacement vectors, magnitude and direction.

Coordinate Geometry, Vectors and TrigonometryS2 B.1S2 B.2S2 B.3S2 B.4S2 B.5S2 B.6S2 B.7S2 B.8≈ 45 min🎮 3 games
Before you start

By the end of this lesson you can…

Step 1 · Watch

Explainer video

5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.

LESSON B3 · EXPLAINER

Vectors in Two Dimensions: i, j Notation, Magnitude and Direction

A plane flies at 300 km/h — but in which direction? Quantities with direction are vectors, and i, j notation lets you calculate with them like algebra.

Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.

Explore in 3D

Vectors

Change the components and see a + b.

Step 2 · Read

Key notes

Copy these into your notebook in your own words — that is how they stick.

Scalar vs vector

Scalar: size only. Vector: size and direction.

Notation

a = xi + yj = (x over y); i = (1, 0), j = (0, 1).

Operations

Add/subtract/scale component by component.

Equal / parallel

Equal: same components. Parallel: a = λb.

Magnitude

|a| = √(x² + y²).

Unit vector

â = a/|a|.

Displacement

AB = OB − OA.

Direction

tan θ = y/x (adjust for quadrant); bearing from North.

EXAM TIPS & COMMON MISTAKES

  • AB = OB − OA: end minus start.
  • To find a unit vector divide BOTH components by the magnitude.
  • Sketch the vector to choose the correct quadrant for the angle.
  • Two vectors are parallel when the components are in the same ratio: 2i − 3j and −4i + 6j.
Play & practise

Games

3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Additional Mathematics Arcade.

Step 3 · Practise

Paper 1 practice — multiple choice

8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.

Adapted from CSEC P1 May/June 2024 (unit vector item)

1. The vector a = 5i + 12j. A unit vector parallel to a is

Answer: C. |a| = 13.
CSEC Paper 01 style · SO B.4

2. If a = 3i − 2j and b = −i + 5j then a + b is

Answer: D. (3 − 1)i + (−2 + 5)j.
CSEC Paper 01 style · SO B.5

3. If a = 3i − 2j and b = −i + 5j then 2a − b is

Answer: A. 6i − 4j + i − 5j.
CSEC Paper 01 style · SO B.8

4. The magnitude of 3i + 4j is

Answer: A. √25.
CSEC Paper 01 style · SO B.7

5. A(1, 2) and B(5, 5). The displacement vector AB is

Answer: B. OB − OA.
CSEC Paper 01 style · SO B.2

6. Which vector is parallel to 2i − 3j?

Answer: C. −2(2i − 3j).
CSEC Paper 01 style · SO B.8

7. The angle that 3i + 4j makes with the positive x-axis is closest to

Answer: D. tan⁻¹(4/3).
CSEC Paper 01 style · SO B.1

8. Which of the following is a vector quantity?

Answer: A. Velocity has a direction.
Step 4 · Apply

Paper 2 practice — structured questions

Write full answers, then reveal the mark scheme and tick the points you earned (26 marks in total). Show all your working — method marks count. Your answers are saved on this device.

CSEC Paper 02 style · Section 2 (Vectors)

Question 1 [14 marks]

a = 3i − 2j and b = −i + 5j.

(a) Find a + b, 2a − b and |a|. [5]

MARK SCHEME — (a) (max 5)

(b) Write down the unit vector in the direction of b. [3]

MARK SCHEME — (b) (max 3)

(c) Find the value of λ for which a + λb is parallel to the vector i. [3]

MARK SCHEME — (c) (max 3)

(d) Find the angle that b makes with the positive x-axis, to 1 decimal place. [3]

MARK SCHEME — (d) (max 3)

CSEC Paper 02 style · Section 2 (Position vectors)

Question 2 [12 marks]

O is the origin, A is (4, 1) and B is (1, 5).

(a) Write down OA and OB, and find AB and |AB|. [5]

MARK SCHEME — (a) (max 5)

(b) M is the midpoint of AB. Find OM. [2]

MARK SCHEME — (b) (max 2)

(c) OACB is a parallelogram. Find OC. [2]

MARK SCHEME — (c) (max 2)

(d) A boat moves with velocity (6i + 8j) km/h in a current of (−2i + j) km/h. Find the resultant velocity and the actual speed. [3]

MARK SCHEME — (d) (max 3)

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Sources

Where this topic appears in CSEC papers

Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.