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O Level Additional Mathematics Algebra Functions Quiz
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O-Level Additional Mathematics Quiz - Algebra Functions
Answer Key and Marking Scheme
Total Marks: 50
Section A: Quadratic Functions and Equations (Questions 1–5)
1. ( y = 3x^2 - 12x + 7 )
- Factor out 3: ( y = 3(x^2 - 4x) + 7 ) [M1]
- Complete the square: ( y = 3[(x - 2)^2 - 4] + 7 = 3(x - 2)^2 - 12 + 7 ) [M1]
- ( y = 3(x - 2)^2 - 5 )
- Minimum value is (-5), occurring at ( x = 2 ) [A1]
- Total: 3 marks
2. ( 2x^2 + kx + 8 = 0 )
- For no real roots, discriminant ( b^2 - 4ac < 0 ) [M1]
- ( k^2 - 4(2)(8) < 0 \implies k^2 - 64 < 0 ) [M1]
- ( (k - 8)(k + 8) < 0 \implies -8 < k < 8 ) [A1]
- Total: 3 marks
3. ( f(x) = x^2 + px + q ), minimum (-4) at ( x = 3 )
- Completed square form: ( f(x) = (x - 3)^2 - 4 ) [M1]
- Expanding: ( f(x) = x^2 - 6x + 9 - 4 = x^2 - 6x + 5 )
- Therefore ( p = -6 ), ( q = 5 ) [A1]
- Total: 2 marks
4. ( x^2 - 5x + 6 \leq 0 )
- Factorise: ( (x - 2)(x - 3) \leq 0 ) [M1]
- Critical values: ( x = 2 ), ( x = 3 )
- Solution: ( 2 \leq x \leq 3 ) [A1]
- Number line: closed circles at 2 and 3, shaded between.
- Total: 2 marks
5. Points: ((1, 4)), ((2, 9)), ((-1, 6))
- Substitute into ( y = ax^2 + bx + c ):
- ( a + b + c = 4 ) ... (1)
- ( 4a + 2b + c = 9 ) ... (2)
- ( a - b + c = 6 ) ... (3) [M1]
- (1) - (3): ( 2b = -2 \implies b = -1 )
- Substitute ( b = -1 ) into (1): ( a - 1 + c = 4 \implies a + c = 5 )
- Substitute into (2): ( 4a - 2 + c = 9 \implies 4a + c = 11 )
- Solving: ( 3a = 6 \implies a = 2 ), ( c = 3 )
- ( a = 2 ), ( b = -1 ), ( c = 3 ) [A1]
- Total: 2 marks
Section B: Surds and Indices (Questions 6–10)
6. ( \sqrt{75} - \sqrt{27} + \sqrt{48} )
- ( \sqrt{75} = 5\sqrt{3} ), ( \sqrt{27} = 3\sqrt{3} ), ( \sqrt{48} = 4\sqrt{3} ) [M1]
- ( 5\sqrt{3} - 3\sqrt{3} + 4\sqrt{3} = 6\sqrt{3} ) [A1]
- Total: 2 marks
7. ( \displaystyle \frac{4}{3 - \sqrt{5}} )
- Multiply by conjugate: ( \displaystyle \frac{4}{3 - \sqrt{5}} \times \frac{3 + \sqrt{5}}{3 + \sqrt{5}} ) [M1]
- ( = \frac{4(3 + \sqrt{5})}{9 - 5} = \frac{12 + 4\sqrt{5}}{4} = 3 + \sqrt{5} ) [A1]
- Total: 2 marks
8. ( \displaystyle \frac{\sqrt{2} + 1}{\sqrt{2} - 1} )
- Multiply by conjugate: ( \displaystyle \frac{(\sqrt{2} + 1)^2}{(\sqrt{2} - 1)(\sqrt{2} + 1)} ) [M1]
- Numerator: ( (\sqrt{2} + 1)^2 = 2 + 2\sqrt{2} + 1 = 3 + 2\sqrt{2} ) [M1]
- Denominator: ( 2 - 1 = 1 )
- ( = 3 + 2\sqrt{2} ), so ( a = 3 ), ( b = 2 ) [A1]
- Total: 3 marks
9. ( \sqrt{2x + 5} - \sqrt{x - 1} = 2 )
- Rearrange: ( \sqrt{2x + 5} = 2 + \sqrt{x - 1} ) [M1]
- Square both sides: ( 2x + 5 = 4 + 4\sqrt{x - 1} + (x - 1) )
- ( 2x + 5 = x + 3 + 4\sqrt{x - 1} )
- ( x + 2 = 4\sqrt{x - 1} ) [M1]
- Square again: ( (x + 2)^2 = 16(x - 1) )
- ( x^2 + 4x + 4 = 16x - 16 )
- ( x^2 - 12x + 20 = 0 )
- ( (x - 2)(x - 10) = 0 \implies x = 2 ) or ( x = 10 )
- Check: ( x = 2 ): ( \sqrt{9} - \sqrt{1} = 3 - 1 = 2 ) ✓
- ( x = 10 ): ( \sqrt{25} - \sqrt{9} = 5 - 3 = 2 ) ✓ [M1]
- Both solutions valid: ( x = 2 ) or ( x = 10 ) [A1]
- Total: 3 marks
10. ( \displaystyle \frac{1}{\sqrt{3} - 1} )
- Rationalise: ( \displaystyle \frac{1}{\sqrt{3} - 1} \times \frac{\sqrt{3} + 1}{\sqrt{3} + 1} = \frac{\sqrt{3} + 1}{3 - 1} = \frac{\sqrt{3} + 1}{2} ) [M1]
- ( = \frac{1.732 + 1}{2} = \frac{2.732}{2} = 1.366 \approx 1.37 ) (3 s.f.) [A1]
- Total: 2 marks
Section C: Polynomials and Partial Fractions (Questions 11–15)
11. ( P(x) = 2x^3 - 5x^2 + ax + b )
- ( P(2) = 5 ): ( 2(8) - 5(4) + 2a + b = 5 \implies 16 - 20 + 2a + b = 5 \implies 2a + b = 9 ) ... (1) [M1]
- ( P(-1) = -10 ): ( 2(-1) - 5(1) + a(-1) + b = -10 \implies -2 - 5 - a + b = -10 \implies -a + b = -3 ) ... (2) [M1]
- (1) - (2): ( 3a = 12 \implies a = 4 )
- Substitute: ( 2(4) + b = 9 \implies b = 1 )
- ( a = 4 ), ( b = 1 ) [A1]
- Total: 3 marks
12. ( P(x) = x^3 - 4x^2 - 7x + k ), factor ( (x - 3) )
- ( P(3) = 0 ): ( 27 - 36 - 21 + k = 0 \implies k = 30 ) [M1]
- ( P(x) = x^3 - 4x^2 - 7x + 30 )
- Divide by ( (x - 3) ): ( P(x) = (x - 3)(x^2 - x - 10) ) [M1]
- Quadratic discriminant: ( 1 + 40 = 41 ), does not factorise over integers.
- Complete factorisation: ( (x - 3)(x^2 - x - 10) ) [A1]
- Total: 3 marks
13. ( \displaystyle \frac{7x - 1}{(x + 2)(x - 3)} )
- Let ( \displaystyle \frac{7x - 1}{(x + 2)(x - 3)} = \frac{A}{x + 2} + \frac{B}{x - 3} ) [M1]
- ( 7x - 1 = A(x - 3) + B(x + 2) )
- ( x = 3 ): ( 20 = 5B \implies B = 4 )
- ( x = -2 ): ( -15 = -5A \implies A = 3 )
- ( \displaystyle \frac{3}{x + 2} + \frac{4}{x - 3} ) [A1]
- Total: 2 marks
14. ( \displaystyle \frac{2x^2 + 5x + 4}{(x + 1)(x^2 + 1)} )
- Let ( \displaystyle \frac{2x^2 + 5x + 4}{(x + 1)(x^2 + 1)} = \frac{A}{x + 1} + \frac{Bx + C}{x^2 + 1} ) [M1]
- ( 2x^2 + 5x + 4 = A(x^2 + 1) + (Bx + C)(x + 1) )
- ( = Ax^2 + A + Bx^2 + Bx + Cx + C )
- ( = (A + B)x^2 + (B + C)x + (A + C) ) [M1]
- Compare coefficients:
- ( A + B = 2 ) ... (1)
- ( B + C = 5 ) ... (2)
- ( A + C = 4 ) ... (3)
- (1) - (3): ( B - C = -2 ) ... (4)
- (2) + (4): ( 2B = 3 \implies B = 1.5 )
- From (1): ( A = 0.5 )
- From (2): ( C = 3.5 )
- ( \displaystyle \frac{0.5}{x + 1} + \frac{1.5x + 3.5}{x^2 + 1} ) or ( \displaystyle \frac{1}{2(x + 1)} + \frac{3x + 7}{2(x^2 + 1)} ) [A1]
- Total: 3 marks
15. ( x^3 - 6x^2 + 11x - 6 = 0 ), factor ( (x - 1) )
- Divide by ( (x - 1) ): ( (x - 1)(x^2 - 5x + 6) = 0 ) [M1]
- Factorise quadratic: ( (x - 1)(x - 2)(x - 3) = 0 )
- Solutions: ( x = 1, 2, 3 ) [A1]
- Total: 2 marks
Section D: Binomial Expansions and Exponential/Logarithmic Functions (Questions 16–20)
16. ( (3 + 2x)^6 )
- General term: ( \binom{6}{r} 3^{6-r} (2x)^r = \binom{6}{r} 3^{6-r} 2^r x^r ) [M1]
- For ( x^4 ), ( r = 4 ): ( \binom{6}{4} 3^{2} 2^4 = 15 \times 9 \times 16 = 2160 )
- Coefficient is 2160 [A1]
- Total: 2 marks
17. ( (1 + kx)^8 ), coefficient of ( x^3 ) is 1512
- General term: ( \binom{8}{r} 1^{8-r} (kx)^r = \binom{8}{r} k^r x^r ) [M1]
- For ( x^3 ), ( r = 3 ): ( \binom{8}{3} k^3 = 56k^3 ) [M1]
- ( 56k^3 = 1512 \implies k^3 = 27 \implies k = 3 ) [A1]
- Total: 3 marks
18. ( 3^{2x+1} = 5^{x-2} )
- Take ( \ln ) of both sides: ( (2x + 1)\ln 3 = (x - 2)\ln 5 ) [M1]
- ( 2x\ln 3 + \ln 3 = x\ln 5 - 2\ln 5 )
- ( 2x\ln 3 - x\ln 5 = -2\ln 5 - \ln 3 ) [M1]
- ( x(2\ln 3 - \ln 5) = -(2\ln 5 + \ln 3) )
- ( x = \frac{-(2\ln 5 + \ln 3)}{2\ln 3 - \ln 5} = \frac{2\ln 5 + \ln 3}{\ln 5 - 2\ln 3} )
- ( x = \frac{2(1.6094) + 1.0986}{1.6094 - 2(1.0986)} = \frac{4.3174}{-0.5878} \approx -7.35 ) [A1]
- Total: 3 marks
19. ( \log_2(x + 3) - \log_2(x - 1) = 3 )
- ( \log_2\left(\frac{x + 3}{x - 1}\right) = 3 ) [M1]
- ( \frac{x + 3}{x - 1} = 2^3 = 8 ) [M1]
- ( x + 3 = 8(x - 1) \implies x + 3 = 8x - 8 \implies 7x = 11 \implies x = \frac{11}{7} )
- Check domain: ( x + 3 > 0 ) and ( x - 1 > 0 \implies x > 1 ). ( \frac{11}{7} \approx 1.57 > 1 ) ✓ [M1]
- ( x = \frac{11}{7} ) [A1]
- Total: 3 marks
20. ( M = M_0 e^{-kt} ), ( M_0 = 80 ), ( M = 50 ) when ( t = 5 )
- ( 50 = 80e^{-5k} \implies e^{-5k} = \frac{50}{80} = 0.625 ) [M1]
- ( -5k = \ln(0.625) \implies k = -\frac{\ln(0.625)}{5} = \frac{\ln(1.6)}{5} )
- ( k = \frac{0.4700}{5} = 0.0940 ) (3 s.f.) [A1]
- Total: 2 marks
END OF ANSWER KEY