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O Level Additional Mathematics Graphs Coordinate Geometry Quiz

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O-Level Additional Mathematics Quiz - Graphs Coordinate Geometry

ANSWER KEY AND MARKING SCHEME

Total Marks: 50


Section A: Basic Coordinate Geometry (15 marks)

1. Midpoint = (−3+52,7+(−1)2)\left(\frac{-3+5}{2}, \frac{7+(-1)}{2}\right) [M1]
= (1,3)(1, 3) [A1]
[2 marks]


2. Rearranging 2x−3y+6=02x - 3y + 6 = 0:
3y=2x+63y = 2x + 6
y=23x+2y = \frac{2}{3}x + 2 [M1]
Gradient = 23\frac{2}{3} [A1]
[2 marks]


3. Gradient of y=3x−2y = 3x - 2 is 33.
Rearranging 6x−2y+5=06x - 2y + 5 = 0: 2y=6x+52y = 6x + 5, so y=3x+52y = 3x + \frac{5}{2}. [M1]
Gradient is 33.
Since both gradients are equal (m1=m2=3m_1 = m_2 = 3), the lines are parallel. [A1]
[2 marks]


4. Gradient of given line is 12\frac{1}{2}.
Gradient of perpendicular line = −2-2 (since m1×m2=−1m_1 \times m_2 = -1). [M1]
Using point (2,−1)(2, -1): y−(−1)=−2(x−2)y - (-1) = -2(x - 2) [M1]
y+1=−2x+4y + 1 = -2x + 4
2x+y−3=02x + y - 3 = 0 [A1]
[3 marks]


5. Using the shoelace formula:
12∣1(8−2)+5(2−2)+9(2−8)∣\frac{1}{2}|1(8-2) + 5(2-2) + 9(2-8)| [M1]
=12∣1(6)+5(0)+9(−6)∣= \frac{1}{2}|1(6) + 5(0) + 9(-6)| [M1]
=12∣6−54∣=12∣−48∣=24= \frac{1}{2}|6 - 54| = \frac{1}{2}|-48| = 24 square units [A1]
[3 marks]


6. Distance = (4−(−2))2+(−3−5)2\sqrt{(4-(-2))^2 + (-3-5)^2} [M1]
=62+(−8)2= \sqrt{6^2 + (-8)^2} [M1]
=36+64=100=10= \sqrt{36 + 64} = \sqrt{100} = 10 [A1]
[3 marks]


Section B: Circles (15 marks)

7. x2+y2−6x+4y−12=0x^2 + y^2 - 6x + 4y - 12 = 0
Completing the square:
(x2−6x)+(y2+4y)=12(x^2 - 6x) + (y^2 + 4y) = 12
(x−3)2−9+(y+2)2−4=12(x - 3)^2 - 9 + (y + 2)^2 - 4 = 12 [M1]
(x−3)2+(y+2)2=25(x - 3)^2 + (y + 2)^2 = 25 [M1]
Centre = (3,−2)(3, -2) [A1]
Radius = 25=5\sqrt{25} = 5 [A1]
[4 marks]


8. Centre (−2,3)(-2, 3), radius 55:
(x−(−2))2+(y−3)2=52(x - (-2))^2 + (y - 3)^2 = 5^2 [M1]
(x+2)2+(y−3)2=25(x + 2)^2 + (y - 3)^2 = 25 [M1]
Expanding: x2+4x+4+y2−6y+9=25x^2 + 4x + 4 + y^2 - 6y + 9 = 25
x2+y2+4x−6y−12=0x^2 + y^2 + 4x - 6y - 12 = 0 [A1]
[3 marks]


9. Centre is midpoint of ABAB: (1+72,4+(−2)2)=(4,1)\left(\frac{1+7}{2}, \frac{4+(-2)}{2}\right) = (4, 1) [M1]
Radius = half the distance ABAB:
AB=(7−1)2+(−2−4)2=36+36=72=62AB = \sqrt{(7-1)^2 + (-2-4)^2} = \sqrt{36 + 36} = \sqrt{72} = 6\sqrt{2} [M1]
Radius = 323\sqrt{2}
Equation: (x−4)2+(y−1)2=(32)2=18(x - 4)^2 + (y - 1)^2 = (3\sqrt{2})^2 = 18 [M1]
x2+y2−8x−2y+16+1−18=0x^2 + y^2 - 8x - 2y + 16 + 1 - 18 = 0
x2+y2−8x−2y−1=0x^2 + y^2 - 8x - 2y - 1 = 0 [A1]
[4 marks]


10. Distance from centre (3,−1)(3, -1) to point (6,3)(6, 3):
r=(6−3)2+(3−(−1))2r = \sqrt{(6-3)^2 + (3-(-1))^2} [M1]
=32+42= \sqrt{3^2 + 4^2} [M1]
=9+16= \sqrt{9 + 16} [M1]
=25=5= \sqrt{25} = 5 units [A1]
[4 marks]


Section C: Intersections and Applications (20 marks)

11. Equating: 2x+1=x2−x−32x + 1 = x^2 - x - 3 [M1]
x2−3x−4=0x^2 - 3x - 4 = 0 [M1]
(x−4)(x+1)=0(x - 4)(x + 1) = 0 [M1]
x=4x = 4 or x=−1x = -1
When x=4x = 4: y=2(4)+1=9y = 2(4) + 1 = 9
When x=−1x = -1: y=2(−1)+1=−1y = 2(-1) + 1 = -1 [M1]
Points: (4,9)(4, 9) and (−1,−1)(-1, -1) [A1]
[5 marks]


12. For tangency, equate and set discriminant = 0:
mx+2=x2+3x+1mx + 2 = x^2 + 3x + 1 [M1]
x2+(3−m)x−1=0x^2 + (3 - m)x - 1 = 0 [M1]
Discriminant = (3−m)2−4(1)(−1)=0(3 - m)^2 - 4(1)(-1) = 0 [M1]
(3−m)2+4=0(3 - m)^2 + 4 = 0
(3−m)2=−4(3 - m)^2 = -4
No real solutions. [M1]
Wait — check: x2+3x+1−mx−2=0x^2 + 3x + 1 - mx - 2 = 0
x2+(3−m)x−1=0x^2 + (3 - m)x - 1 = 0
Discriminant = (3−m)2−4(1)(−1)=(3−m)2+4(3 - m)^2 - 4(1)(-1) = (3 - m)^2 + 4
For tangency: (3−m)2+4=0(3 - m)^2 + 4 = 0, which has no real solutions.
Therefore, no real value of mm exists for which the line is tangent. [A1]

Alternative interpretation: The line y=mx+2y = mx + 2 cannot be tangent to y=x2+3x+1y = x^2 + 3x + 1 because the discriminant is always positive.
[5 marks]


13. (a) Centre of CC is (2,−1)(2, -1).
Substitute into LL: y=2(2)−5=−1y = 2(2) - 5 = -1 [M1]
Since y=−1y = -1 matches the yy-coordinate of the centre, LL passes through the centre. [A1]
[2 marks]

(b) Substitute y=2x−5y = 2x - 5 into (x−2)2+(y+1)2=25(x - 2)^2 + (y + 1)^2 = 25:
(x−2)2+(2x−5+1)2=25(x - 2)^2 + (2x - 5 + 1)^2 = 25 [M1]
(x−2)2+(2x−4)2=25(x - 2)^2 + (2x - 4)^2 = 25
(x−2)2+4(x−2)2=25(x - 2)^2 + 4(x - 2)^2 = 25 [M1]
5(x−2)2=255(x - 2)^2 = 25
(x−2)2=5(x - 2)^2 = 5 [M1]
x−2=±5x - 2 = \pm\sqrt{5}
x=2±5x = 2 \pm \sqrt{5}
When x=2+5x = 2 + \sqrt{5}: y=2(2+5)−5=4+25−5=−1+25y = 2(2 + \sqrt{5}) - 5 = 4 + 2\sqrt{5} - 5 = -1 + 2\sqrt{5}
When x=2−5x = 2 - \sqrt{5}: y=2(2−5)−5=4−25−5=−1−25y = 2(2 - \sqrt{5}) - 5 = 4 - 2\sqrt{5} - 5 = -1 - 2\sqrt{5} [M1]
Points: (2+5,−1+25)(2 + \sqrt{5}, -1 + 2\sqrt{5}) and (2−5,−1−25)(2 - \sqrt{5}, -1 - 2\sqrt{5}) [A1]
[4 marks]


14. (a) Equating: 6x=7−x\frac{6}{x} = 7 - x [M1]
6=7x−x26 = 7x - x^2
x2−7x+6=0x^2 - 7x + 6 = 0 [M1]
(x−1)(x−6)=0(x - 1)(x - 6) = 0
x=1x = 1 or x=6x = 6
When x=1x = 1: y=7−1=6y = 7 - 1 = 6
When x=6x = 6: y=7−6=1y = 7 - 6 = 1
Points: (1,6)(1, 6) and (6,1)(6, 1) [A1]
[3 marks]

(b) There are 2 intersection points. [A1]
[1 mark]


15. (a) Midpoint of ACAC: (2+52,1+72)=(3.5,4)\left(\frac{2+5}{2}, \frac{1+7}{2}\right) = (3.5, 4) [M1]
Midpoint of BDBD: (6+12,3+52)=(3.5,4)\left(\frac{6+1}{2}, \frac{3+5}{2}\right) = (3.5, 4) [M1]
Since the diagonals bisect each other, ABCDABCD is a parallelogram. [A1]
[3 marks]

(b) Gradient of ABAB: 3−16−2=24=12\frac{3-1}{6-2} = \frac{2}{4} = \frac{1}{2} [M1]
Gradient of BCBC: 7−35−6=4−1=−4\frac{7-3}{5-6} = \frac{4}{-1} = -4
Product of gradients = 12×(−4)=−2≠−1\frac{1}{2} \times (-4) = -2 \neq -1
Therefore, adjacent sides are not perpendicular, so ABCDABCD is not a rectangle. [A1]
[2 marks]


16. Equating: 2x+k=x2+4x−12x + k = x^2 + 4x - 1 [M1]
x2+2x−(1+k)=0x^2 + 2x - (1 + k) = 0 [M1]
For two distinct points, discriminant > 0:
22−4(1)(−(1+k))>02^2 - 4(1)(-(1+k)) > 0 [M1]
4+4(1+k)>04 + 4(1 + k) > 0
4+4+4k>04 + 4 + 4k > 0 [M1]
4k>−84k > -8
k>−2k > -2 [A1]
[5 marks]


17. Original circle: x2+y2−4x+6y−3=0x^2 + y^2 - 4x + 6y - 3 = 0
Completing the square: (x−2)2+(y+3)2=16(x - 2)^2 + (y + 3)^2 = 16 [M1]
Centre is (2,−3)(2, -3), radius = 44.
Reflection in yy-axis: xx-coordinate changes sign. [M1]
New centre: (−2,−3)(-2, -3)
Equation: (x+2)2+(y+3)2=16(x + 2)^2 + (y + 3)^2 = 16 [M1]
Expanding: x2+4x+4+y2+6y+9=16x^2 + 4x + 4 + y^2 + 6y + 9 = 16
x2+y2+4x+6y−3=0x^2 + y^2 + 4x + 6y - 3 = 0 [A1]
[4 marks]


18. (a) Since PQPQ is parallel to the xx-axis, yy-coordinates are equal:
p2−2p+5=q2−2q+5p^2 - 2p + 5 = q^2 - 2q + 5 [M1]
p2−2p=q2−2qp^2 - 2p = q^2 - 2q
(p2−q2)−2(p−q)=0(p^2 - q^2) - 2(p - q) = 0
(p−q)(p+q)−2(p−q)=0(p - q)(p + q) - 2(p - q) = 0
(p−q)(p+q−2)=0(p - q)(p + q - 2) = 0
Since p≠qp \neq q, p+q−2=0p + q - 2 = 0, so q=2−pq = 2 - p [A1]
[2 marks]

(b) Length PQ=∣p−q∣=∣p−(2−p)∣PQ = |p - q| = |p - (2 - p)| [M1]
=∣2p−2∣=2∣p−1∣= |2p - 2| = 2|p - 1| [A1]
[2 marks]


19. Substitute y=x+1y = x + 1 into x2+y2=25x^2 + y^2 = 25:
x2+(x+1)2=25x^2 + (x + 1)^2 = 25 [M1]
x2+x2+2x+1=25x^2 + x^2 + 2x + 1 = 25
2x2+2x−24=02x^2 + 2x - 24 = 0 [M1]
x2+x−12=0x^2 + x - 12 = 0
(x+4)(x−3)=0(x + 4)(x - 3) = 0 [M1]
x=−4x = -4 or x=3x = 3
When x=−4x = -4: y=−3y = -3; when x=3x = 3: y=4y = 4
Points: A(−4,−3)A(-4, -3) and B(3,4)B(3, 4) [M1]
Length AB=(3−(−4))2+(4−(−3))2=72+72=98=49×2=72AB = \sqrt{(3-(-4))^2 + (4-(-3))^2} = \sqrt{7^2 + 7^2} = \sqrt{98} = \sqrt{49 \times 2} = 7\sqrt{2}
=98= \sqrt{98} [A1]
[5 marks]


20. Turning point at (−1,0)(-1, 0):
y=a(x+1)2+0y = a(x + 1)^2 + 0 (completed square form) [M1]
y=a(x2+2x+1)=ax2+2ax+ay = a(x^2 + 2x + 1) = ax^2 + 2ax + a [M1]
Passes through (1,4)(1, 4):
4=a(1)2+2a(1)+a4 = a(1)^2 + 2a(1) + a [M1]
4=a+2a+a=4a4 = a + 2a + a = 4a
a=1a = 1 [M1]
Therefore: y=x2+2x+1y = x^2 + 2x + 1
So a=1a = 1, b=2b = 2, c=1c = 1 [A1]
[5 marks]


END OF ANSWER KEY