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O Level Elementary Mathematics Vectors Matrices Quiz
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O-Level Elementary Mathematics Quiz - Vectors Matrices
Answer Key and Marking Scheme
Total Marks: 50
Section A: Matrices (25 marks)
1. (a) Order of P is 2 × 2. ✓ [1 mark]
(b) Element in second row, first column = 5. ✓ [1 mark]
2. (a) A + B = (\begin{pmatrix} 4+(-1) & 1+5 \ -3+2 & 2+0 \end{pmatrix} = \begin{pmatrix} 3 & 6 \ -1 & 2 \end{pmatrix}) ✓✓ [2 marks: 1 for correct addition, 1 for correct result]
(b) 3A = (\begin{pmatrix} 3×4 & 3×1 \ 3×(-3) & 3×2 \end{pmatrix} = \begin{pmatrix} 12 & 3 \ -9 & 6 \end{pmatrix}) ✓✓ [2 marks]
3. CD = (\begin{pmatrix} 2 & -1 \ 0 & 3 \end{pmatrix} \begin{pmatrix} 1 & 4 \ -2 & 1 \end{pmatrix})
= (\begin{pmatrix} 2(1)+(-1)(-2) & 2(4)+(-1)(1) \ 0(1)+3(-2) & 0(4)+3(1) \end{pmatrix})
= (\begin{pmatrix} 2+2 & 8-1 \ 0-6 & 0+3 \end{pmatrix} = \begin{pmatrix} 4 & 7 \ -6 & 3 \end{pmatrix}) ✓✓✓ [3 marks: 1 for correct method, 1 for correct row 1, 1 for correct row 2]
4. (a) S = (\begin{pmatrix} 24 & 18 & 30 \ 20 & 25 & 22 \end{pmatrix}) ✓ [1 mark]
(b) P = (\begin{pmatrix} 0.80 \ 0.50 \ 0.60 \end{pmatrix}) ✓ [1 mark]
(c) Revenue = S × P = (\begin{pmatrix} 24(0.80)+18(0.50)+30(0.60) \ 20(0.80)+25(0.50)+22(0.60) \end{pmatrix})
= (\begin{pmatrix} 19.20+9.00+18.00 \ 16.00+12.50+13.20 \end{pmatrix} = \begin{pmatrix} 46.20 \ 41.70 \end{pmatrix})
Monday: 41.70 ✓✓ [2 marks: 1 for correct multiplication, 1 for correct values]
5. For M = (\begin{pmatrix} 5 & 2 \ 3 & 1 \end{pmatrix}):
Determinant = 5(1) - 2(3) = 5 - 6 = -1 ✓
M⁻¹ = (\frac{1}{-1} \begin{pmatrix} 1 & -2 \ -3 & 5 \end{pmatrix} = \begin{pmatrix} -1 & 2 \ 3 & -5 \end{pmatrix}) ✓✓ [3 marks: 1 for determinant, 1 for adjugate, 1 for final answer]
6. Write as matrix equation: (\begin{pmatrix} 3 & 2 \ 1 & -4 \end{pmatrix} \begin{pmatrix} x \ y \end{pmatrix} = \begin{pmatrix} 7 \ -14 \end{pmatrix}) ✓
Determinant = 3(-4) - 2(1) = -12 - 2 = -14 ✓
Inverse = (\frac{1}{-14} \begin{pmatrix} -4 & -2 \ -1 & 3 \end{pmatrix})
(\begin{pmatrix} x \ y \end{pmatrix} = \frac{1}{-14} \begin{pmatrix} -4 & -2 \ -1 & 3 \end{pmatrix} \begin{pmatrix} 7 \ -14 \end{pmatrix})
= (\frac{1}{-14} \begin{pmatrix} -28+28 \ -7-42 \end{pmatrix} = \frac{1}{-14} \begin{pmatrix} 0 \ -49 \end{pmatrix} = \begin{pmatrix} 0 \ 3.5 \end{pmatrix}) ✓✓
x = 0, y = 3.5 [4 marks: 1 for matrix form, 1 for determinant, 1 for inverse, 1 for solution]
7. (a) N represents an enlargement with scale factor 2, centre at the origin. ✓ [1 mark]
(b) N² = (\begin{pmatrix} 2 & 0 \ 0 & 2 \end{pmatrix} \begin{pmatrix} 2 & 0 \ 0 & 2 \end{pmatrix} = \begin{pmatrix} 4 & 0 \ 0 & 4 \end{pmatrix}) ✓✓ [2 marks: 1 for method, 1 for result]
8. 2X + Z = Y → Z = Y - 2X ✓
2X = (\begin{pmatrix} 2 & 6 \ 4 & 8 \end{pmatrix})
Z = (\begin{pmatrix} -1 & 2 \ 0 & 5 \end{pmatrix} - \begin{pmatrix} 2 & 6 \ 4 & 8 \end{pmatrix} = \begin{pmatrix} -3 & -4 \ -4 & -3 \end{pmatrix}) ✓✓ [3 marks: 1 for rearranging, 1 for 2X, 1 for Z]
9. Transform each vertex:
A' = T(\begin{pmatrix} 1 \ 2 \end{pmatrix} = \begin{pmatrix} 0 & -1 \ 1 & 0 \end{pmatrix} \begin{pmatrix} 1 \ 2 \end{pmatrix} = \begin{pmatrix} -2 \ 1 \end{pmatrix}) ✓
B' = T(\begin{pmatrix} 3 \ 2 \end{pmatrix} = \begin{pmatrix} -2 \ 3 \end{pmatrix}) ✓
C' = T(\begin{pmatrix} 2 \ 5 \end{pmatrix} = \begin{pmatrix} -5 \ 2 \end{pmatrix}) ✓ [3 marks: 1 for each correct image]
10. Determinant = 4(3) - 2(6) = 12 - 12 = 0 ✓
Since the determinant is zero, the matrix is singular and does not have an inverse. ✓ [2 marks: 1 for determinant, 1 for conclusion with reason]
Section B: Vectors (25 marks)
11. (a) a + b = (\begin{pmatrix} 3+(-1) \ -2+4 \end{pmatrix} = \begin{pmatrix} 2 \ 2 \end{pmatrix}) ✓ [1 mark]
(b) 2a - 3b = (\begin{pmatrix} 6 \ -4 \end{pmatrix} - \begin{pmatrix} -3 \ 12 \end{pmatrix} = \begin{pmatrix} 9 \ -16 \end{pmatrix}) ✓✓ [2 marks: 1 for scalar multiplication, 1 for subtraction]
12. (a) (\overrightarrow{PQ} = \overrightarrow{OQ} - \overrightarrow{OP} = \begin{pmatrix} -3-2 \ 1-5 \end{pmatrix} = \begin{pmatrix} -5 \ -4 \end{pmatrix}) ✓ [1 mark]
(b) |(\overrightarrow{PQ})| = (\sqrt{(-5)^2 + (-4)^2} = \sqrt{25+16} = \sqrt{41} \approx 6.40) ✓✓ [2 marks: 1 for formula, 1 for correct value to 3 s.f.]
13. (a) (\overrightarrow{OB} = \overrightarrow{OA} + \overrightarrow{OC} = \mathbf{a} + \mathbf{c}) ✓ [1 mark]
(b) (\overrightarrow{OM} = \overrightarrow{OA} + \frac{1}{2}\overrightarrow{AB} = \mathbf{a} + \frac{1}{2}\mathbf{c}) ✓✓ [2 marks: 1 for identifying AB = c, 1 for expression]
(c) (\overrightarrow{ON} = \overrightarrow{OC} + \frac{1}{3}\overrightarrow{CB} = \mathbf{c} + \frac{1}{3}\mathbf{a}) ✓✓ [2 marks: 1 for ratio, 1 for expression]
14. u + v = (\begin{pmatrix} 4+(-2) \ 1+3 \end{pmatrix} = \begin{pmatrix} 2 \ 4 \end{pmatrix}) ✓
Magnitude = (\sqrt{2^2 + 4^2} = \sqrt{4+16} = \sqrt{20} = 2\sqrt{5}) ✓
Unit vector = (\frac{1}{2\sqrt{5}} \begin{pmatrix} 2 \ 4 \end{pmatrix} = \begin{pmatrix} \frac{1}{\sqrt{5}} \ \frac{2}{\sqrt{5}} \end{pmatrix}) ✓ [3 marks: 1 for sum, 1 for magnitude, 1 for unit vector]
15. (\overrightarrow{AB} = \begin{pmatrix} 5-1 \ 7-3 \end{pmatrix} = \begin{pmatrix} 4 \ 4 \end{pmatrix}) ✓
(\overrightarrow{BC} = \begin{pmatrix} 9-5 \ 11-7 \end{pmatrix} = \begin{pmatrix} 4 \ 4 \end{pmatrix}) ✓
Since (\overrightarrow{AB} = \overrightarrow{BC}), the vectors are parallel and share point B, so A, B, and C are collinear. ✓ [3 marks: 1 for AB, 1 for BC, 1 for conclusion with reasoning]
16. For parallel vectors, p = λq for some scalar λ.
(\begin{pmatrix} 2 \ -5 \end{pmatrix} = \lambda \begin{pmatrix} k \ 10 \end{pmatrix})
From second component: -5 = 10λ → λ = -0.5 ✓
From first component: 2 = -0.5k → k = -4 ✓ [2 marks: 1 for λ, 1 for k]
17. (a) Translation vector = (\begin{pmatrix} 7-3 \ 2-(-1) \end{pmatrix} = \begin{pmatrix} 4 \ 3 \end{pmatrix}) ✓ [1 mark]
(b) Image = (\begin{pmatrix} -2+4 \ 5+3 \end{pmatrix} = \begin{pmatrix} 2 \ 8 \end{pmatrix}) ✓ [1 mark]
18. (a) (\overrightarrow{BC} = \overrightarrow{BA} + \overrightarrow{AC} = -\overrightarrow{AB} + \overrightarrow{AC} = \begin{pmatrix} -4 \ 1 \end{pmatrix} + \begin{pmatrix} 1 \ 3 \end{pmatrix} = \begin{pmatrix} -3 \ 4 \end{pmatrix}) ✓ [1 mark]
(b) |AB| = (\sqrt{4^2+(-1)^2} = \sqrt{17})
|AC| = (\sqrt{1^2+3^2} = \sqrt{10})
|BC| = (\sqrt{(-3)^2+4^2} = \sqrt{25} = 5) ✓
Check if right-angled: |AB|² + |AC|² = 17 + 10 = 27; |BC|² = 25. Not equal.
|AB|² + |BC|² = 17 + 25 = 42; |AC|² = 10. Not equal.
|AC|² + |BC|² = 10 + 25 = 35; |AB|² = 17. Not equal.
All sides have different lengths, so triangle ABC is scalene. ✓ [2 marks: 1 for side lengths, 1 for correct classification with reasoning]
19. Using section formula: T divides RS in ratio 3:2.
(\overrightarrow{OT} = \frac{2\mathbf{r} + 3\mathbf{s}}{3+2} = \frac{2\begin{pmatrix} 6 \ -2 \end{pmatrix} + 3\begin{pmatrix} -4 \ 8 \end{pmatrix}}{5})
= (\frac{\begin{pmatrix} 12 \ -4 \end{pmatrix} + \begin{pmatrix} -12 \ 24 \end{pmatrix}}{5} = \frac{\begin{pmatrix} 0 \ 20 \end{pmatrix}}{5} = \begin{pmatrix} 0 \ 4 \end{pmatrix}) ✓✓✓ [3 marks: 1 for formula, 1 for substitution, 1 for result]
20. (a) Speed = |v| = (\sqrt{5^2 + 12^2} = \sqrt{25+144} = \sqrt{169} = 13) km/h ✓ [1 mark]
(b) tan θ = 12/5 → θ = tan⁻¹(2.4) ≈ 67.38° ✓
Bearing = 90° - 67.38° = 022.6° (or N22.6°E) ✓ [2 marks: 1 for angle, 1 for bearing to 1 d.p.]
END OF ANSWER KEY