O-Level Additional Mathematics Quiz - Algebra Functions (Answer Key)
Total Marks: 40
Topic: Algebra Functions (syllabus-first practice from inferred templates; not past-year derived)
Section A: Quadratic Functions and Discriminant
1. [2 marks]
Complete the square:
y = x 2 − 6 x + 10 = ( x 2 − 6 x + 9 ) + 1 = ( x − 3 ) 2 + 1 y = x^2 - 6x + 10 = (x^2 - 6x + 9) + 1 = (x - 3)^2 + 1 y = x 2 − 6 x + 10 = ( x 2 − 6 x + 9 ) + 1 = ( x − 3 ) 2 + 1 .
Since ( x − 3 ) 2 ≥ 0 (x - 3)^2 \ge 0 ( x − 3 ) 2 ≥ 0 , minimum value is 1 1 1 when x = 3 x = 3 x = 3 .
Teaching note: Completing the square reveals vertex form y = a ( x − h ) 2 + k y = a(x-h)^2 + k y = a ( x − h ) 2 + k ; minimum is k k k if a > 0 a>0 a > 0 .
Answer: Minimum value = 1 .
2. [2 marks]
Two distinct real roots ⇒ discriminant > 0 > 0 > 0 :
Δ = k 2 − 4 ( 1 ) ( 4 ) = k 2 − 16 > 0 \Delta = k^2 - 4(1)(4) = k^2 - 16 > 0 Δ = k 2 − 4 ( 1 ) ( 4 ) = k 2 − 16 > 0 ⇒ k 2 > 16 k^2 > 16 k 2 > 16 ⇒ k < − 4 k < -4 k < − 4 or k > 4 k > 4 k > 4 .
Answer: k < − 4 k < -4 k < − 4 or k > 4 k > 4 k > 4 .
3. [2 marks]
Always positive ⇒ a > 0 a > 0 a > 0 (here 2 > 0 2 > 0 2 > 0 ) and Δ < 0 \Delta < 0 Δ < 0 .
Δ = ( − 3 ) 2 − 4 ( 2 ) ( c ) = 9 − 8 c < 0 \Delta = (-3)^2 - 4(2)(c) = 9 - 8c < 0 Δ = ( − 3 ) 2 − 4 ( 2 ) ( c ) = 9 − 8 c < 0 .
Answer: 9 − 8 c < 0 9 - 8c < 0 9 − 8 c < 0 (or c > 9 8 c > \frac{9}{8} c > 8 9 ).
4. [2 marks]
y = − x 2 + 4 x − 1 = − ( x 2 − 4 x ) − 1 = − ( x 2 − 4 x + 4 − 4 ) − 1 = − ( x − 2 ) 2 + 4 − 1 = − ( x − 2 ) 2 + 3 y = -x^2 + 4x - 1 = -(x^2 - 4x) - 1 = -(x^2 - 4x + 4 - 4) - 1 = -(x - 2)^2 + 4 - 1 = -(x - 2)^2 + 3 y = − x 2 + 4 x − 1 = − ( x 2 − 4 x ) − 1 = − ( x 2 − 4 x + 4 − 4 ) − 1 = − ( x − 2 ) 2 + 4 − 1 = − ( x − 2 ) 2 + 3 .
Vertex: ( 2 , 3 ) (2, 3) ( 2 , 3 ) .
Answer: y = − ( x − 2 ) 2 + 3 y = -(x - 2)^2 + 3 y = − ( x − 2 ) 2 + 3 , vertex ( 2 , 3 ) (2, 3) ( 2 , 3 ) .
5. [2 marks]
Tangent ⇒ one point ⇒ discriminant = 0 = 0 = 0 .
x 2 + 2 x + 3 = m x + 1 x^2 + 2x + 3 = mx + 1 x 2 + 2 x + 3 = m x + 1 ⇒ x 2 + ( 2 − m ) x + 2 = 0 x^2 + (2 - m)x + 2 = 0 x 2 + ( 2 − m ) x + 2 = 0 .
Δ = ( 2 − m ) 2 − 8 = 0 \Delta = (2 - m)^2 - 8 = 0 Δ = ( 2 − m ) 2 − 8 = 0 ⇒ ( 2 − m ) 2 = 8 (2 - m)^2 = 8 ( 2 − m ) 2 = 8 ⇒ 2 − m = ± 2 2 2 - m = \pm 2\sqrt{2} 2 − m = ± 2 2 ⇒ m = 2 ∓ 2 2 m = 2 \mp 2\sqrt{2} m = 2 ∓ 2 2 .
Answer: m = 2 − 2 2 m = 2 - 2\sqrt{2} m = 2 − 2 2 or m = 2 + 2 2 m = 2 + 2\sqrt{2} m = 2 + 2 2 .
Section B: Equations, Inequalities and Surds
6. [2 marks]
x + 1 = x 2 − 3 x + 1 x + 1 = x^2 - 3x + 1 x + 1 = x 2 − 3 x + 1 ⇒ x 2 − 4 x = 0 x^2 - 4x = 0 x 2 − 4 x = 0 ⇒ x ( x − 4 ) = 0 x(x - 4) = 0 x ( x − 4 ) = 0 ⇒ x = 0 x = 0 x = 0 or x = 4 x = 4 x = 4 .
When x = 0 x = 0 x = 0 , y = 1 y = 1 y = 1 ; when x = 4 x = 4 x = 4 , y = 5 y = 5 y = 5 .
Answer: ( 0 , 1 ) (0, 1) ( 0 , 1 ) and ( 4 , 5 ) (4, 5) ( 4 , 5 ) .
7. [2 marks]
x 2 − 5 x + 6 = ( x − 2 ) ( x − 3 ) < 0 x^2 - 5x + 6 = (x - 2)(x - 3) < 0 x 2 − 5 x + 6 = ( x − 2 ) ( x − 3 ) < 0 ⇒ 2 < x < 3 2 < x < 3 2 < x < 3 .
Number line: open circles at 2 and 3, shaded between.
Answer: 2 < x < 3 2 < x < 3 2 < x < 3 .
8. [2 marks]
12 = 2 3 \sqrt{12} = 2\sqrt{3} 12 = 2 3 , 27 = 3 3 \sqrt{27} = 3\sqrt{3} 27 = 3 3 ⇒ 2 3 + 3 3 = 5 3 2\sqrt{3} + 3\sqrt{3} = 5\sqrt{3} 2 3 + 3 3 = 5 3 .
Answer: 5 3 5\sqrt{3} 5 3 .
9. [2 marks]
2 3 − 1 × 3 + 1 3 + 1 = 2 ( 3 + 1 ) 3 − 1 = 2 ( 3 + 1 ) 2 = 3 + 1 \dfrac{2}{\sqrt{3} - 1} \times \dfrac{\sqrt{3} + 1}{\sqrt{3} + 1} = \dfrac{2(\sqrt{3} + 1)}{3 - 1} = \dfrac{2(\sqrt{3} + 1)}{2} = \sqrt{3} + 1 3 − 1 2 × 3 + 1 3 + 1 = 3 − 1 2 ( 3 + 1 ) = 2 2 ( 3 + 1 ) = 3 + 1 .
Answer: 3 + 1 \sqrt{3} + 1 3 + 1 .
10. [2 marks]
Square both sides: x + 3 = ( x − 3 ) 2 = x 2 − 6 x + 9 x + 3 = (x - 3)^2 = x^2 - 6x + 9 x + 3 = ( x − 3 ) 2 = x 2 − 6 x + 9 ⇒ x 2 − 7 x + 6 = 0 x^2 - 7x + 6 = 0 x 2 − 7 x + 6 = 0 ⇒ ( x − 1 ) ( x − 6 ) = 0 (x - 1)(x - 6) = 0 ( x − 1 ) ( x − 6 ) = 0 .
Check: x = 1 x = 1 x = 1 ⇒ 4 = 2 \sqrt{4} = 2 4 = 2 , RHS = − 2 = -2 = − 2 (reject); x = 6 x = 6 x = 6 ⇒ 9 = 3 \sqrt{9} = 3 9 = 3 , RHS = 3 = 3 = 3 (valid).
Answer: x = 6 x = 6 x = 6 .
Section C: Polynomials, Partial Fractions and Binomial
11. [2 marks]
Remainder theorem: remainder = P ( 2 ) = 2 3 − 4 ( 2 ) 2 + 2 + 6 = 8 − 16 + 2 + 6 = 0 = P(2) = 2^3 - 4(2)^2 + 2 + 6 = 8 - 16 + 2 + 6 = 0 = P ( 2 ) = 2 3 − 4 ( 2 ) 2 + 2 + 6 = 8 − 16 + 2 + 6 = 0 .
Answer: 0.
12. [2 marks]
Let P ( x ) = x 3 − 3 x 2 − 4 x + 12 P(x) = x^3 - 3x^2 - 4x + 12 P ( x ) = x 3 − 3 x 2 − 4 x + 12 . P ( 3 ) = 27 − 27 − 12 + 12 = 0 P(3) = 27 - 27 - 12 + 12 = 0 P ( 3 ) = 27 − 27 − 12 + 12 = 0 ⇒ ( x − 3 ) (x - 3) ( x − 3 ) is a factor.
Answer: Shown.
13. [2 marks]
5 ( x + 1 ) ( x − 2 ) = A x + 1 + B x − 2 \dfrac{5}{(x+1)(x-2)} = \dfrac{A}{x+1} + \dfrac{B}{x-2} ( x + 1 ) ( x − 2 ) 5 = x + 1 A + x − 2 B .
5 = A ( x − 2 ) + B ( x + 1 ) 5 = A(x - 2) + B(x + 1) 5 = A ( x − 2 ) + B ( x + 1 ) .
x = − 1 x = -1 x = − 1 : 5 = − 3 A 5 = -3A 5 = − 3 A ⇒ A = − 5 3 A = -\frac{5}{3} A = − 3 5 .
x = 2 x = 2 x = 2 : 5 = 3 B 5 = 3B 5 = 3 B ⇒ B = 5 3 B = \frac{5}{3} B = 3 5 .
Answer: − 5 3 ( x + 1 ) + 5 3 ( x − 2 ) -\dfrac{5}{3(x+1)} + \dfrac{5}{3(x-2)} − 3 ( x + 1 ) 5 + 3 ( x − 2 ) 5 .
14. [2 marks]
( 1 + 2 x ) 4 = ( 4 0 ) 1 4 + ( 4 1 ) 1 3 ( 2 x ) + ( 4 2 ) 1 2 ( 2 x ) 2 + ⋯ = 1 + 8 x + 24 x 2 + ⋯ (1 + 2x)^4 = \binom{4}{0}1^4 + \binom{4}{1}1^3(2x) + \binom{4}{2}1^2(2x)^2 + \cdots = 1 + 8x + 24x^2 + \cdots ( 1 + 2 x ) 4 = ( 0 4 ) 1 4 + ( 1 4 ) 1 3 ( 2 x ) + ( 2 4 ) 1 2 ( 2 x ) 2 + ⋯ = 1 + 8 x + 24 x 2 + ⋯
Answer: 1 + 8 x + 24 x 2 1 + 8x + 24x^2 1 + 8 x + 24 x 2 (first three terms).
15. [2 marks]
General term: ( 5 r ) 2 5 − r ( − x ) r \binom{5}{r}2^{5-r}(-x)^r ( r 5 ) 2 5 − r ( − x ) r . For x 3 x^3 x 3 , r = 3 r = 3 r = 3 : ( 5 3 ) 2 2 ( − 1 ) 3 = 10 × 4 × ( − 1 ) = − 40 \binom{5}{3}2^2(-1)^3 = 10 \times 4 \times (-1) = -40 ( 3 5 ) 2 2 ( − 1 ) 3 = 10 × 4 × ( − 1 ) = − 40 .
Answer: − 40 -40 − 40 .
Section D: Exponential and Logarithmic Functions
16. [2 marks]
2 x = 16 = 2 4 2^x = 16 = 2^4 2 x = 16 = 2 4 ⇒ x = 4 x = 4 x = 4 .
Answer: x = 4 x = 4 x = 4 .
17. [2 marks]
log 2 ( x + 1 ) = 3 \log_2(x + 1) = 3 log 2 ( x + 1 ) = 3 ⇒ x + 1 = 2 3 = 8 x + 1 = 2^3 = 8 x + 1 = 2 3 = 8 ⇒ x = 7 x = 7 x = 7 .
Answer: x = 7 x = 7 x = 7 .
18. [2 marks]
log a ( b 2 / c ) = 2 log a b − log a c = 2 ( 2 ) − 3 = 1 \log_a(b^2/c) = 2\log_a b - \log_a c = 2(2) - 3 = 1 log a ( b 2 / c ) = 2 log a b − log a c = 2 ( 2 ) − 3 = 1 .
Answer: 1 1 1 (independent of a a a ).
19. [2 marks]
e 2 x = 5 e^{2x} = 5 e 2 x = 5 ⇒ 2 x = ln 5 2x = \ln 5 2 x = ln 5 ⇒ x = 1 2 ln 5 x = \frac{1}{2}\ln 5 x = 2 1 ln 5 .
Answer: x = ln 5 2 x = \frac{\ln 5}{2} x = 2 l n 5 .
20. [2 marks]
log 4 8 = log 2 8 log 2 4 = 3 2 \log_4 8 = \dfrac{\log_2 8}{\log_2 4} = \dfrac{3}{2} log 4 8 = log 2 4 log 2 8 = 2 3 .
Answer: 3 2 \dfrac{3}{2} 2 3 .