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Secondary 4 Elementary Mathematics Algebra Functions Quiz
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Secondary 4 Elementary Mathematics Quiz - Algebra Functions
ANSWER KEY AND MARKING SCHEME
Total Marks: 50
Section A: Quadratic Functions and Graphs (Questions 1–7)
1. ( y = x^2 - 6x + 5 )
- ( y = (x^2 - 6x + 9) - 9 + 5 ) [1 mark for completing square]
- ( y = (x - 3)^2 - 4 ) [1 mark for correct form]
- Turning point: ( (3, -4) ) [½ mark]
- Line of symmetry: ( x = 3 ) [½ mark] Total: 3 marks
2. ( y = -(x + 2)^2 + 9 )
- Turning point: ( (-2, 9) ) — maximum point [1 mark]
- y-intercept: when ( x = 0 ), ( y = -(2)^2 + 9 = 5 ); point ( (0, 5) ) [1 mark]
- x-intercepts: ( -(x + 2)^2 + 9 = 0 ); ( (x + 2)^2 = 9 ); ( x + 2 = \pm 3 ); ( x = 1 ) or ( x = -5 ); points ( (1, 0) ) and ( (-5, 0) ) [1 mark]
- Correct n-shaped parabola with all key points labelled [1 mark] Total: 4 marks
3. ( y = (x - a)(x - b) ) with x-intercepts at ( x = -3 ) and ( x = 5 )
- ( a = -3, b = 5 ) (or vice versa) [1 mark]
- Axis of symmetry: ( x = \frac{-3 + 5}{2} = 1 ) [½ mark]
- When ( x = 1 ): ( y = (1 + 3)(1 - 5) = 4 \times (-4) = -16 ) [1 mark]
- Turning point: ( (1, -16) ) [½ mark] Total: 3 marks
4. ( y = 2x^2 - 8x + 3 ) (a) ( y = 2(x^2 - 4x) + 3 ) ( y = 2(x^2 - 4x + 4 - 4) + 3 ) ( y = 2(x - 2)^2 - 8 + 3 ) ( y = 2(x - 2)^2 - 5 ) [2 marks for correct form] (b) Minimum value: ( y = -5 ) when ( x = 2 ) [1 mark for value, 1 mark for x-coordinate] Total: 4 marks
5. ( y = x^2 + px + q ) passes through ( (1, -2) ) and ( (3, 4) )
- At ( (1, -2) ): ( 1 + p + q = -2 ); ( p + q = -3 ) ... (1) [½ mark]
- At ( (3, 4) ): ( 9 + 3p + q = 4 ); ( 3p + q = -5 ) ... (2) [½ mark]
- (2) - (1): ( 2p = -2 ); ( p = -1 ) [½ mark]
- Substitute: ( -1 + q = -3 ); ( q = -2 ) [½ mark] Total: 2 marks
6. Maximum value 8 when ( x = -1 ), passes through ( (1, 0) )
- Vertex form: ( y = a(x + 1)^2 + 8 ) (since maximum, ( a < 0 )) [1 mark]
- Substitute ( (1, 0) ): ( 0 = a(2)^2 + 8 ); ( 4a = -8 ); ( a = -2 ) [½ mark]
- Equation: ( y = -2(x + 1)^2 + 8 ) [½ mark] Total: 2 marks
7. ( y = x^2 - 4x - 5 = (x - 5)(x + 1) )
- x-intercepts: ( x = -1 ) and ( x = 5 ) [½ mark]
- Parabola opens upward (u-shaped) [½ mark]
- ( x^2 - 4x - 5 \le 0 ) means the curve is on or below the x-axis [½ mark]
- Solution: ( -1 \le x \le 5 ) [½ mark] Total: 2 marks
Section B: Power Functions and Exponential Functions (Questions 8–13)
8. ( y = \frac{4}{x} ) for ( x > 0 )
- Asymptotes: ( x = 0 ) (y-axis) and ( y = 0 ) (x-axis) [1 mark]
- As ( x \to \infty ), ( y \to 0^+ ) (approaches 0 from above) [1 mark]
- Correct sketch: decreasing curve in first quadrant, approaching both axes [1 mark] Total: 3 marks
9. ( y = ax^3 ) passes through ( (2, 24) )
- ( 24 = a(2)^3 = 8a ); ( a = 3 ) [1 mark]
- Equation: ( y = 3x^3 ) [½ mark]
- Correct sketch: S-shaped curve through origin, passing through ( (-3, -81) ), ( (-2, -24) ), ( (-1, -3) ), ( (0, 0) ), ( (1, 3) ), ( (2, 24) ), ( (3, 81) ) [1½ marks] Total: 3 marks
10. ( y = 3 \times 2^x ) (a) Table:
- ( x = -2 ): ( y = 3 \times 2^{-2} = 3 \times \frac{1}{4} = 0.75 )
- ( x = -1 ): ( y = 3 \times 2^{-1} = 1.5 )
- ( x = 0 ): ( y = 3 \times 1 = 3 )
- ( x = 1 ): ( y = 3 \times 2 = 6 )
- ( x = 2 ): ( y = 3 \times 4 = 12 )
- ( x = 3 ): ( y = 3 \times 8 = 24 ) [2 marks for correct table] (b) Correct sketch: exponential growth curve, y-intercept at ( (0, 3) ), passing through all table points [2 marks] (c) From graph, when ( y = 10 ), ( x \approx 1.7 ) (accept 1.6 to 1.8) [1 mark] Total: 5 marks
11. ( y = k \times 3^x ) passes through ( (2, 36) )
- ( 36 = k \times 3^2 = 9k ); ( k = 4 ) [1 mark] Total: 1 mark
12. Graphs of ( y = x^2 ) and ( y = x^3 ) for ( -2 \le x \le 2 )
- Correct sketch of both curves on same axes [1 mark]
- Intersection points: ( x^2 = x^3 ); ( x^2(1 - x) = 0 ); ( x = 0 ) or ( x = 1 ) [½ mark]
- Coordinates: ( (0, 0) ) and ( (1, 1) ) [½ mark] Total: 2 marks
13. ( y = \frac{8}{x^2} ) for ( x \neq 0 )
- Asymptote: ( x = 0 ) (y-axis) and ( y = 0 ) (x-axis) [1 mark]
- As ( x \to 0^+ ), ( y \to +\infty ) (increases without bound) [1 mark] Total: 2 marks
Section C: Gradient of Curves and Applications (Questions 14–20)
14. ( y = x^2 + 2x - 3 ) at ( x = 2 )
- When ( x = 2 ), ( y = 4 + 4 - 3 = 5 ); point ( (2, 5) ) [½ mark]
- Tangent drawn at ( (2, 5) ) [½ mark]
- Gradient estimated from tangent: rise/run [1 mark]
- Expected gradient: approximately 6 (accept 5.5 to 6.5) [1 mark] Total: 3 marks
15. ( d = 2t^2 + 5t )
- When ( t = 3 ), ( d = 2(9) + 15 = 33 ); point ( (3, 33) ) [½ mark]
- Tangent drawn at ( t = 3 ) [½ mark]
- Gradient estimated: approximately 17 (accept 16 to 18) [1 mark]
- Interpretation: The gradient represents the speed (or instantaneous velocity) of the car at ( t = 3 ) seconds, in m/s [1 mark] Total: 3 marks
16. ( y = 4x - x^2 ), tangent at ( P(1, 3) )
- When ( x = 1 ), ( y = 4 - 1 = 3 ) ✓ [½ mark]
- Tangent drawn at ( P(1, 3) ) [½ mark]
- Gradient of tangent estimated: approximately 2 (accept 1.5 to 2.5) [½ mark]
- Equation of tangent: ( y - 3 = 2(x - 1) ); ( y = 2x + 1 ) [½ mark]
- At x-axis, ( y = 0 ): ( 0 = 2x + 1 ); ( x = -0.5 ) [½ mark]
- Coordinates of ( Q ): ( (-0.5, 0) ) [½ mark] Total: 3 marks
17. ( y = x^3 - 3x )
- At ( x = -1 ): ( y = -1 + 3 = 2 ); gradient ≈ 0 (tangent horizontal) [1 mark]
- At ( x = 0 ): ( y = 0 ); gradient ≈ -3 (tangent sloping down) [½ mark]
- At ( x = 1 ): ( y = 1 - 3 = -2 ); gradient ≈ 0 (tangent horizontal) [1 mark]
- Points where gradient appears zero: ( (-1, 2) ) and ( (1, -2) ) [½ mark] Total: 3 marks
18. ( v = 10 + 8t - t^2 ) at ( t = 4 )
- When ( t = 4 ), ( v = 10 + 32 - 16 = 26 ); point ( (4, 26) ) [½ mark]
- Tangent drawn at ( t = 4 ) [½ mark]
- Gradient estimated: approximately 0 (accept -1 to 1) [½ mark]
- Acceleration = gradient of speed-time graph = 0 m/s² [½ mark] Total: 2 marks
19. ( y = \frac{12}{x} ) at ( x = 3 )
- When ( x = 3 ), ( y = 4 ); point ( (3, 4) ) [½ mark]
- Tangent drawn at ( (3, 4) ) [½ mark]
- Gradient estimated: approximately -1.3 (accept -1.1 to -1.5) [1 mark]
- Answer to 1 d.p.: -1.3 [½ mark] Total: 2 marks
20. ( y = x^2 - 6x + 8 ), tangent at ( x = 4 )
- When ( x = 4 ), ( y = 16 - 24 + 8 = 0 ); point ( (4, 0) ) [½ mark]
- Tangent drawn at ( (4, 0) ) [½ mark]
- Gradient estimated: approximately 2 (accept 1.5 to 2.5) [½ mark]
- Equation of tangent: ( y - 0 = 2(x - 4) ); ( y = 2x - 8 ) [½ mark]
- At y-axis, ( x = 0 ): ( y = -8 ) [½ mark]
- Coordinates of ( R ): ( (0, -8) ) [½ mark] Total: 3 marks
END OF ANSWER KEY