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O Level Additional Mathematics Practice Paper 3
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TuitionGoWhere Practice Paper - Additional Mathematics O-Level
Answer Key and Marking Scheme
Paper: Practice Paper 3 (Graphs & Coordinate Geometry)
Total Marks: 90
Section A (45 marks)
Question 1
(a) Length of AB [2 marks]
AB = √[(4 − (−2))² + (−3 − 5)²]
= √[6² + (−8)²]
= √(36 + 64)
= √100
= 10 units [M1, A1]
(b) Midpoint of AB [1 mark]
Midpoint = ((−2 + 4)/2, (5 + (−3))/2) = (1, 1) [B1]
(c) Perpendicular bisector of AB [4 marks]
Gradient of AB = (−3 − 5)/(4 − (−2)) = −8/6 = −4/3 [M1]
Gradient of perpendicular bisector = 3/4 [M1]
Perpendicular bisector passes through midpoint (1, 1).
Equation: y − 1 = (3/4)(x − 1)
4y − 4 = 3x − 3
3x − 4y + 1 = 0 [M1, A1]
Question 2
(a) Gradient of L [1 mark]
Line 2x − 5y + 7 = 0 → 5y = 2x + 7 → y = (2/5)x + 7/5
Gradient = 2/5. Since L is parallel, gradient of L = 2/5. [B1]
(b) Equation of L [2 marks]
y − (−1) = (2/5)(x − 3) [M1]
y + 1 = (2/5)x − 6/5
y = (2/5)x − 11/5 [A1]
(c) Intersection with x-axis [2 marks]
At x-axis, y = 0.
0 = (2/5)x − 11/5 [M1]
(2/5)x = 11/5
x = 11/2 = 5.5
Coordinates: (5.5, 0) [A1]
Question 3
(a) Show PQ ⟂ PR [3 marks]
Gradient of PQ = (8 − 2)/(5 − 1) = 6/4 = 3/2 [M1]
Gradient of PR = (4 − 2)/(−3 − 1) = 2/(−4) = −1/2 [M1]
Product of gradients = (3/2) × (−1/2) = −3/4 ≠ −1.
Correction: Let me recalculate.
P(1, 2), Q(5, 8), R(−3, 4)
Gradient PQ = (8 − 2)/(5 − 1) = 6/4 = 3/2
Gradient PR = (4 − 2)/(−3 − 1) = 2/(−4) = −1/2
Product = (3/2)(−1/2) = −3/4
This does not equal −1. Let me check the coordinates again.
P(1, 2), Q(5, 8), R(−3, 4)
Vector PQ = (4, 6), Vector PR = (−4, 2)
Dot product = 4(−4) + 6(2) = −16 + 12 = −4 ≠ 0.
The points as given do not produce perpendicular lines. Let me adjust the answer to reflect the correct calculation:
Gradient of PQ = (8 − 2)/(5 − 1) = 6/4 = 3/2 [M1]
Gradient of PR = (4 − 2)/(−3 − 1) = 2/(−4) = −1/2 [M1]
Product = (3/2)(−1/2) = −3/4 ≠ −1, so PQ is not perpendicular to PR. [A1 for correct calculation and conclusion]
Note: If the question intended perpendicular lines, coordinates should be adjusted. With given coordinates, the correct conclusion is that they are not perpendicular.
(b) Area of triangle PQR [3 marks]
Using the shoelace formula:
Area = ½|x₁(y₂ − y₃) + x₂(y₃ − y₁) + x₃(y₁ − y₂)| [M1]
= ½|1(8 − 4) + 5(4 − 2) + (−3)(2 − 8)|
= ½|1(4) + 5(2) + (−3)(−6)| [M1]
= ½|4 + 10 + 18|
= ½(32)
= 16 square units [A1]
Question 4
(a) Centre and radius of C [3 marks]
x² + y² − 6x + 10y + 9 = 0
Complete the square:
(x² − 6x) + (y² + 10y) = −9
(x − 3)² − 9 + (y + 5)² − 25 = −9 [M1]
(x − 3)² + (y + 5)² = 25 [M1]
Centre: (3, −5), Radius: 5 units [A1]
(b) Tangent at A(7, −2) [4 marks]
Centre C(3, −5).
Gradient of CA = (−2 − (−5))/(7 − 3) = 3/4 [M1]
Gradient of tangent = −4/3 (perpendicular to radius) [M1]
Equation: y − (−2) = (−4/3)(x − 7)
y + 2 = (−4/3)x + 28/3
3y + 6 = −4x + 28 [M1]
4x + 3y − 22 = 0 [A1]
Question 5
(a) Quadratic equation in x [2 marks]
Substitute y = 2x + k into x² + y² − 4x + 2y − 20 = 0:
x² + (2x + k)² − 4x + 2(2x + k) − 20 = 0 [M1]
x² + 4x² + 4kx + k² − 4x + 4x + 2k − 20 = 0
5x² + 4kx + k² + 2k − 20 = 0 [A1]
(b) Possible values of k [4 marks]
For tangency, discriminant = 0.
a = 5, b = 4k, c = k² + 2k − 20
b² − 4ac = (4k)² − 4(5)(k² + 2k − 20) = 0 [M1]
16k² − 20(k² + 2k − 20) = 0
16k² − 20k² − 40k + 400 = 0
−4k² − 40k + 400 = 0 [M1]
k² + 10k − 100 = 0
k = [−10 ± √(100 + 400)]/2 = [−10 ± √500]/2 = [−10 ± 10√5]/2 = −5 ± 5√5 [M1, A1]
Question 6
(a) Show ABCD is a parallelogram [3 marks]
A(−1, 4), B(3, −2), C(7, 2), D(3, 8)
Midpoint of AC = ((−1 + 7)/2, (4 + 2)/2) = (3, 3) [M1]
Midpoint of BD = ((3 + 3)/2, (−2 + 8)/2) = (3, 3) [M1]
Since the diagonals bisect each other, ABCD is a parallelogram. [A1]
(b) Area of parallelogram ABCD [4 marks]
Vector AB = (4, −6), Vector AD = (4, 4) [M1]
Area = |det(AB, AD)| = |4(4) − (−6)(4)| [M1]
= |16 + 24| [M1]
= 40 square units [A1]
Alternative using shoelace formula accepted.
Section B (45 marks)
Question 7
(a) Stationary points [4 marks]
y = x³ − 6x² + 9x + 1
dy/dx = 3x² − 12x + 9 = 3(x² − 4x + 3) = 3(x − 1)(x − 3) [M1]
Stationary points when dy/dx = 0: x = 1 or x = 3 [M1]
When x = 1: y = 1 − 6 + 9 + 1 = 5 → (1, 5) [A1]
When x = 3: y = 27 − 54 + 27 + 1 = 1 → (3, 1) [A1]
(b) Nature of stationary points [3 marks]
d²y/dx² = 6x − 12 [M1]
At x = 1: d²y/dx² = 6 − 12 = −6 < 0 → maximum [A1]
At x = 3: d²y/dx² = 18 − 12 = 6 > 0 → minimum [A1]
(c) Normal at x = 2 [4 marks]
When x = 2: y = 8 − 24 + 18 + 1 = 3. Point is (2, 3). [M1]
dy/dx at x = 2: 3(4) − 12(2) + 9 = 12 − 24 + 9 = −3 [M1]
Gradient of normal = 1/3 (perpendicular to tangent) [M1]
Equation: y − 3 = (1/3)(x − 2)
3y − 9 = x − 2
x − 3y + 7 = 0 [A1]
Question 8
(a) Straight line graph [2 marks]
y = axⁿ
Taking logarithms (base 10): lg y = lg a + n lg x [M1]
Plotting lg y against lg x gives a straight line with gradient n and vertical intercept lg a. [A1]
(b) Estimate a and n [4 marks]
| x | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|
| y | 5.6 | 15.6 | 32.0 | 55.9 | 88.2 |
| lg x | 0.301 | 0.477 | 0.602 | 0.699 | 0.778 |
| lg y | 0.748 | 1.193 | 1.505 | 1.747 | 1.945 |
Using points (0.301, 0.748) and (0.778, 1.945):
Gradient n = (1.945 − 0.748)/(0.778 − 0.301) = 1.197/0.477 ≈ 2.51 [M1, A1]
lg a = lg y − n lg x. Using (0.301, 0.748):
lg a = 0.748 − 2.51(0.301) = 0.748 − 0.756 = −0.008 ≈ 0 [M1]
a ≈ 10⁰ = 1. So a ≈ 1.0, n ≈ 2.5. [A1]
Accept values close to a = 1.4, n = 2.5 depending on points chosen.
(c) Estimate y when x = 7 [2 marks]
y = 1.0 × 7²·⁵ = 7²·⁵ = 7² × √7 = 49 × 2.646 ≈ 130 [M1, A1]
Accept answers in the range 125–135.
Question 9
(a) Coordinates of P and Q [5 marks]
Circle: (x − 2)² + (y + 1)² = 25
Line: y = 2x − 5
Substitute: (x − 2)² + (2x − 5 + 1)² = 25
(x − 2)² + (2x − 4)² = 25 [M1]
(x² − 4x + 4) + (4x² − 16x + 16) = 25
5x² − 20x + 20 = 25
5x² − 20x − 5 = 0
x² − 4x − 1 = 0 [M1]
x = [4 ± √(16 + 4)]/2 = [4 ± √20]/2 = [4 ± 2√5]/2 = 2 ± √5 [M1]
x = 2 + √5 ≈ 4.236 or x = 2 − √5 ≈ −0.236 [A1]
When x = 2 + √5: y = 2(2 + √5) − 5 = 4 + 2√5 − 5 = 2√5 − 1
When x = 2 − √5: y = 2(2 − √5) − 5 = 4 − 2√5 − 5 = −2√5 − 1
P and Q: (2 + √5, 2√5 − 1) and (2 − √5, −2√5 − 1) [A1]
(b) Length of chord PQ [3 marks]
PQ = √[(2√5)² + (4√5)²] = √(20 + 80) = √100 = 10 units [M1, A1]
Alternative using Pythagoras with radius and perpendicular distance accepted.
(c) Perpendicular distance from C to L [3 marks]
C(2, −1), L: 2x − y − 5 = 0
Distance = |2(2) − (−1) − 5|/√(2² + (−1)²) [M1]
= |4 + 1 − 5|/√5
= 0/√5 = 0 [M1]
This means the line passes through the centre. Let me recheck.
Line: y = 2x − 5 → 2x − y − 5 = 0
At C(2, −1): 2(2) − (−1) − 5 = 4 + 1 − 5 = 0. Yes, the line passes through the centre.
Distance = 0. [A1]
Note: If the line passes through the centre, the chord is a diameter, and PQ = 10, which matches part (b).
Question 10
(a) Equation of circle [4 marks]
A(−2, 1), B(4, 7) are endpoints of diameter.
Centre = midpoint of AB = ((−2 + 4)/2, (1 + 7)/2) = (1, 4) [M1]
Radius = half of AB = ½√[(4 − (−2))² + (7 − 1)²] = ½√(36 + 36) = ½√72 = ½(6√2) = 3√2 [M1]
r² = (3√2)² = 18
Equation: (x − 1)² + (y − 4)² = 18 [M1, A1]
(b) Show C(6, 3) lies outside [2 marks]
Distance from centre (1, 4) to C(6, 3):
= √[(6 − 1)² + (3 − 4)²] = √(25 + 1) = √26 [M1]
√26 > √18 (since 26 > 18), so C lies outside the circle. [A1]
(c) Length of tangent from C [3 marks]
Let CT be the tangent length, where T is the point of tangency.
CT² = OC² − r² (Pythagoras, since radius ⟂ tangent) [M1]
CT² = 26 − 18 = 8 [M1]
CT = √8 = 2√2 units [A1]
Question 11
(a) Equation of L₁ [2 marks]
Passes through (1, 3), gradient = −2.
y − 3 = −2(x − 1) [M1]
y = −2x + 2 + 3
y = −2x + 5 [A1]
(b) Equation of L₂ [3 marks]
L₂ ⟂ L₁, so gradient of L₂ = ½. [M1]
Passes through (−2, 5):
y − 5 = ½(x − (−2)) [M1]
y − 5 = ½(x + 2)
y = ½x + 1 + 5
y = ½x + 6 [A1]
(c) Intersection of L₁ and L₂ [3 marks]
−2x + 5 = ½x + 6 [M1]
−2x − ½x = 6 − 5
−2.5x = 1
x = −0.4 [M1]
y = −2(−0.4) + 5 = 0.8 + 5 = 5.8
Intersection: (−0.4, 5.8) [A1]
(d) Area of triangle formed by L₁, L₂ and y-axis [4 marks]
y-intercept of L₁: (0, 5)
y-intercept of L₂: (0, 6)
Intersection of L₁ and L₂: (−0.4, 5.8)
The triangle has vertices (0, 5), (0, 6), and (−0.4, 5.8). [M1]
Base on y-axis = 6 − 5 = 1 unit [M1]
Perpendicular height = |−0.4 − 0| = 0.4 units [M1]
Area = ½ × base × height = ½ × 1 × 0.4 = 0.2 square units [A1]
Alternative using shoelace formula accepted.
Question 12
(a) Three equations [3 marks]
Circle: x² + y² + px + qy + r = 0
At (1, 2): 1 + 4 + p + 2q + r = 0 → p + 2q + r = −5 ... (1) [B1]
At (3, −4): 9 + 16 + 3p − 4q + r = 0 → 3p − 4q + r = −25 ... (2) [B1]
At (5, 6): 25 + 36 + 5p + 6q + r = 0 → 5p + 6q + r = −61 ... (3) [B1]
(b) Solve for p, q, r [4 marks]
(2) − (1): 2p − 6q = −20 → p − 3q = −10 ... (4) [M1]
(3) − (2): 2p + 10q = −36 → p + 5q = −18 ... (5) [M1]
(5) − (4): 8q = −8 → q = −1 [M1]
Substitute into (4): p − 3(−1) = −10 → p + 3 = −10 → p = −13
Substitute into (1): −13 + 2(−1) + r = −5 → −15 + r = −5 → r = 10
p = −13, q = −1, r = 10 [A1]
(c) Radius of circle [2 marks]
x² + y² − 13x − y + 10 = 0
Centre: (13/2, 1/2) [M1]
r² = (13/2)² + (1/2)² − 10 = 169/4 + 1/4 − 10 = 170/4 − 10 = 42.5 − 10 = 32.5
r = √32.5 = √(65/2) = √65/√2 = √130/2
Radius = √32.5 ≈ 5.70 units [A1]
Accept exact form √(65/2) or decimal 5.70 (3 s.f.).
END OF MARKING SCHEME