Geometry and Trigonometry

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Geometry & Trigonometry

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UNIT 3: GEOMETRY & TRIGONOMETRY

Practice questions covering cylinders, cones, pyramids, triangles (sine rule, cosine rule, area), sectors, vectors (dot product, cross product, lines, planes, angles), Voronoi diagrams, graph theory (Eulerian, Hamiltonian, MST, Dijkstra), 3D coordinates, trigonometric equations, geometric transformations, and more.

Q1 [EASY]

A right circular cylinder has radius 4 cm and height 9 cm. Find:

(a) Volume

(b) Total surface area.

Answer: (a) V=144π≈452 cm³

(b) SA=104π≈327 cm²

Q2 [EASY]

In triangle ABC, angle A=90°, AB=5cm, AC=12cm. Find BC, angle B, and angle C.

Answer: BC=13 cm; B≈67.4°; C≈22.6°

Q3 [EASY]

A sector has radius 8 cm and angle θ = 1.2 radians. Find:

(a) arc length

(b) area of sector.

Answer: (a) 9.6 cm

(b) 38.4 cm²

Q4 [EASY]

In triangle PQR, PQ=7, QR=10, angle Q=48°. Find PR using the cosine rule.

Answer: PR ≈ 7.42

Q5 [EASY]

Find the exact values of sin(60°), cos(30°), and tan(45°) using the unit circle.

Answer: sin(60°)=√3/2; cos(30°)=√3/2; tan(45°)=1

Q6 [EASY]

State the period and amplitude of:

(a) y=3sin(4x)

(b) y=−2cos(x/3).

Answer: (a) Period=π/2, amp=3

(b) Period=6π, amp=2

Q7 [EASY]

Vector a=[3,−1,2] and b=[−2,4,1]. Find:

(a) a+b

(b) |a|, (c) a·b.

Answer: (a) [1,3,3]

(b) √14≈3.74 (c) −8

Q8 [MEDIUM]

A pyramid has a square base of side 6m and vertical height 8m. Find:

(a) slant height

(b) total surface area

(c) volume.

Answer: (a) ≈8.54 m

(b) ≈138.5 m²

(c) 96 m³

Q9 [MEDIUM]

In triangle ABC: a=9, b=12, c=7. Find:

(a) angle A

(b) area of triangle.

Answer: (a) A≈48.2°

(b) Area≈31.4 sq units

Q10 [MEDIUM]

A Voronoi diagram has sites at A(0,0), B(4,0), C(2,4).

(a) Find the perpendicular bisector of AB.

(b) Find the perpendicular bisector of AC.

(c) Find the circumcentre (Voronoi vertex).

(d) Explain what the Voronoi cell of A represents.

Answer: (a) x=2

(b) y=−x/2+5/2

(c) (2, 1.5)

(d) Points nearer to A than any other site

Q11 [MEDIUM]

Vector r = [2,−1,3] + λ[1,2,−1] is a line. Another line s = [0,3,1] + μ[2,1,1].

(a) Find the angle between the direction vectors.

(b) Show the lines do not intersect (are skew).

Answer: (a) θ=60°

(b) System is inconsistent → lines are skew

Q12 [MEDIUM] [HL]

Graph theory: A graph G has vertices {A,B,C,D,E} and edges {AB,AC,BC,CD,DE,AE}.

(a) State the degree of each vertex.

(b) Is G Eulerian?

(c) Find a Hamiltonian path if one exists.

(d) Find the minimum spanning tree.

Answer: (a) A:3,B:2,C:3,D:2,E:2

(b) Not Eulerian (two odd-degree vertices)

(c) B→A→C→D→E

(d) Any spanning tree

Q13 [MEDIUM]

A cone has base radius 5cm and slant height 13cm.

(a) Find the height.

(b) Find the half-angle at the apex.

(c) Find the volume.

(d) A smaller similar cone has volume 1/8 of the original. Find its dimensions.

Answer: (a) 12 cm

(b) ≈22.6°

(c) 100π≈314 cm³

(d) r=2.5cm, h=6cm

Q14 [MEDIUM]

From a boat, the angle of elevation to the top of a cliff is 28°. After moving 50m closer, the angle is 38°. Find the height of the cliff to the nearest metre.

Answer: h ≈ 116 m

Q15 [MEDIUM]

The unit circle: P is a point at angle 5π/6.

(a) Write the exact coordinates of P.

(b) Hence write exact values of sin(5π/6), cos(5π/6), tan(5π/6).

(c) Solve sin(2θ)=cos(θ) for 0≤θ<2π.

Answer: (a) (−√3/2, 1/2)

(b) sin=1/2, cos=−√3/2, tan=−√3/3

(c) θ=π/6, π/2, 5π/6, 3π/2

Q16 [MEDIUM]

Two vectors: u=[2,3,−1] and v=[1,−2,4].

(a) Find u×v (vector product).

(b) Verify u×v is perpendicular to both u and v.

(c) Find the area of the parallelogram formed by u and v.

Answer: (a) [10,−9,−7]

(b) Verified

(c) √230≈15.2 sq units

Q17 [MEDIUM]

In a 3D room, point A is at (1,0,0), B at (4,3,0), and C at (2,1,5) (all in metres).

(a) Find AB and AC

(b) Find the angle BAC

(c) Find the area of triangle ABC.

Answer: (a) AB=[3,3,0], AC=[1,1,5]

(b) ≈73.2°

(c) ≈10.6 m²

Q18 [HARD]

The diagram shows a compound 3D shape: a cylinder of radius r=2cm, height=3cm, topped by a cone of same base radius and height=2cm.

(a) Find the total volume

(b) Find the total surface area (excluding where they join)

(c) Find the slant height of the cone

(d) If the entire shape is scaled by factor k, find the value of k such that the total volume equals 5× the original.

Answer: (a) 44π/3≈46.1cm³

(b) π(16+4√2)≈64.5cm²

(c) 2√2≈2.83cm

(d) k=∛5≈1.71

Q19 [HARD]

The Voronoi diagram shows 5 sites: A(1,1), B(4,2), C(2,5), D(5,5), E(3,3.5).

(a) Find the equation of the Voronoi edge between sites A and B

(b) Determine which site is nearest to the point P(3.5, 4)

(c) A toxic waste dump must be placed at the point equidistant from A, B, and E (Voronoi vertex). Find its coordinates.

(d) A new site F(6,1) is added. Describe how the Voronoi diagram changes.

Answer: (a) y=−3x+9

(b) Site E

(c) Circumcentre via GDC

(d) New cell for F appears

Q20 [HARD]

The graph shows f(x)=4cos(x/2+π/6) (blue) and g(x)=2sin(x)−1 (red) with intersection points marked ★.

(a) Find the amplitude, period, and phase shift of f

(b) Find all x ∈ [0,4π] where f(x)=g(x) to 3 s.f.

(c) Find the area enclosed between f and g between the first two intersections

(d) Show that g can be written in the form R·sin(x+φ)−1 and find R and φ.

Answer: (a) Amp=4, Period=4π, Phase=π/3 to the right

(b) ≈1.05,3.50,7.33,9.78

(c) Via GDC (d) R=2, φ=0

Q21 [HARD]

Vector product applications: Line L₁: r=[1,2,3]+λ[2,1,−1] and Line L₂: r=[3,1,0]+μ[1,3,2].

(a) Find d₁×d₂ (normal to both)

(b) Find the shortest distance between the lines

(c) Plane π contains L₁ and is parallel to L₂. Find the equation of π

(d) Find the angle between π and the xy-plane.

Answer: (a) [1,−1,1]

(b) Lines intersect (dist=0)

(c) Plane via point+normal

(d) Compute via GDC

Q22 [HARD]

A triangular prism has vertices: A(0,0,0), B(4,0,0), C(2,3,0), D(0,0,5), E(4,0,5), F(2,3,5).

(a) Find the length of the space diagonal AE⃗

(b) Find angle DAF (between face AD and diagonal AF)

(c) Find the surface area of the prism

(d) A bug travels from A along the surface to F by the shortest path. Find this distance.

Answer: (a) √41≈6.40

(b) ≈35.7°

(c) 72 sq units

(d) 10 units (by unfolding net)

Q23 [HARD]

Graph Theory: Weighted graph with vertices A,B,C,D,E and edges: AB=3, AC=5, BC=2, BD=6, BE=4, CD=7, DE=3, CE=8.

(a) Find the minimum spanning tree using Kruskal's algorithm. State total weight

(b) Starting from A, apply Dijkstra's algorithm to find shortest path to E

(c) Does an Eulerian circuit exist? Justify

(d) Find a Hamiltonian cycle if possible.

Answer: (a) MST: BC+AB+DE+BE=12

(b) Shortest A→E=7 (via B)

(c) No (C,E odd degree)

(d) ABCDE weight=23

Q24 [HARD]

Sine and cosine rule combined: In a quadrilateral ABCD (vertices in order): AB=6cm, BC=8cm, CD=5cm, DA=7cm, diagonal AC=9cm.

(a) Find angle ABC using cosine rule in triangle ABC

(b) Find the area of triangle ABC

(c) Find angle ADC using cosine rule in triangle ACD

(d) Find the total area of quadrilateral ABCD

(e) Find angle BAD if BD=10.2cm using cosine rule in ABD.

Answer: (a) ≈78.6°

(b) ≈23.5cm²

(c) ≈95.7°

(d) ≈40.9cm²

(e) ≈103.1°

Q25 [HARD]

Matrix M=[[0,−1],[1,0]] represents a rotation.

(a) Show M represents a 90° anticlockwise rotation

(b) Apply M to the triangle with vertices (1,0),(3,0),(2,2) and state the new vertices

(c) Find M⁴ and interpret geometrically

(d) Matrix N=[[0,1],[1,0]] represents a reflection. Find MN and NM and show they represent different transformations.

Answer: (b) (0,1),(0,3),(−2,2)

(c) M⁴=I (identity/360°)

(d) MN≠NM (y-axis vs x-axis reflection)