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IB Diploma Mathematics: Applications & Interpretation SL · Geometry & Trigonometry
Mini-Lesson

Geometry & Trigonometry

This SL mini-lesson covers 3D geometry (distances, angles, volumes & surface areas of solids), right-angled trig (SOH-CAH-TOA), the sine and cosine rules and the area of a triangle, arcs & sectors, and the AI-only topic of Voronoi diagrams.

AI flavour: geometry here is applied — surveying, navigation, packaging and the 'nearest facility' logic of Voronoi diagrams.

Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Every number on the calculation screens has been re-derived and checked. Press Start when you are ready.

Right-angled trig

SOH-CAH-TOA & Pythagoras

In a right-angled triangle with hypotenuse H, opposite O and adjacent A:

sin θ = O⁄H · cos θ = A⁄H · tan θ = O⁄APythagoras: a² + b² = c²

Use inverse functions (sin⁻¹, cos⁻¹, tan⁻¹) to find an angle from a ratio.

Non-right triangles

The sine & cosine rules

For any triangle with sides a, b, c opposite angles A, B, C:

a⁄sin A = b⁄sin B = c⁄sin Ccosine rule: c² = a² + b² − 2ab cos C
Worked example — sine rule

A = 40°, side a = 8, and B = 65°. Find side b.

b = a · sin B ÷ sin A = 8 × sin65° ÷ sin40° = 11.28 (2 d.p.)

Worked example — cosine rule

Sides a = 7, b = 10 with included angle C = 45°.

c² = 7² + 10² − 2×7×10×cos45° = 149 − 98.99 = 50.01, c = 7.07

Calculate

Your turn — sine rule

1In a triangle, A = 40°, side a = 8, and B = 65°. Find side b to 2 decimal places using a⁄sin A = b⁄sin B.
Hint: b = 8 × sin65° ÷ sin40°.
Calculate

Your turn — cosine rule

2A triangle has sides a = 7 and b = 10 with included angle C = 45°. Find side c to 2 decimal places using c² = a² + b² − 2ab cos C.
Hint: c² = 49 + 100 − 140 cos45°, then square-root.
Triangle area

Area with the sine formula

When two sides and the included angle are known:

Area = ½ · a · b · sin Cuse the angle between the two sides
Worked example

a = 7, b = 10, C = 45°.

Area = ½ × 7 × 10 × sin45° = 35 × 0.7071 = 24.75 square units

Calculate

Your turn — triangle area

3Find the area of a triangle with a = 7, b = 10 and included angle C = 45°, to 2 decimal places.
Hint: ½ × 7 × 10 × sin45°.
Quick check

Which rule?

?You know two sides of a triangle and the angle between them, and want the third side. Which rule do you use?
Circles

Arcs & sectors

For a sector of radius r with angle θ in radians:

arc length ℓ = r θsector area = ½ r² θ
Worked example (radians)

r = 6, θ = 1.2 rad.

ℓ = 6 × 1.2 = 7.2

area = ½ × 6² × 1.2 = 21.6

In degrees: ℓ = 2πr × (θ°⁄360) and area = πr² × (θ°⁄360). For r = 5, 60°: ℓ = 5.24, area = 13.09.

Calculate

Your turn — arc length

4A sector has radius r = 6 and angle θ = 1.2 radians. Find the arc length ℓ = r θ.
Hint: 6 × 1.2.
3D geometry

Distances & angles in 3D

The space diagonal of a cuboid with edges a, b, c is √(a²+b²+c²). Angles between a line and a plane are found by dropping to the base and using right-angled trig.

Worked example

A box 4 × 6 × 3. Space diagonal = √(16+36+9) = √61 = 7.81.

Base diagonal = √(16+36) = √52 = 7.21.

Angle of the space diagonal to the base = tan⁻¹(3 ÷ 7.21) = 22.6°

Calculate

Your turn — space diagonal

5A cuboid has edges 4, 6 and 3. Find the length of its space diagonal √(a²+b²+c²), to 2 decimal places.
Hint: √(4² + 6² + 3²) = √61.
Sort it

Which tool fits?

Tap a description, then the trig tool it belongs to.

📐 Right-angled trig

🔺 Sine / cosine rules

⭕ Arcs & sectors

Voronoi diagrams

Voronoi diagrams (nearest neighbour)

A Voronoi diagram partitions a plane around a set of sites so that every point is assigned to its nearest site. Each cell is bounded by perpendicular bisectors of the lines joining neighbouring sites.

Worked example — one edge

Sites at (2, 3) and (6, 7).

Midpoint = ((2+6)⁄2, (3+7)⁄2) = (4, 5)

Segment gradient = (7−3)⁄(6−2) = 1, so bisector gradient = −1

Edge: y − 5 = −1(x − 4) ⇒ y = −x + 9

Toxic-waste / largest-empty-circle: the point furthest from all sites sits at a Voronoi vertex — used to place a new facility as far as possible from existing ones.

Quick check

Voronoi edges

?In a Voronoi diagram, the boundary between two neighbouring sites is always:
Quick check

Radians vs degrees

?The sector formulas ℓ = rθ and area = ½r²θ require the angle θ to be measured in:
Match it

Match the formula to what it finds

Tap an item on the left, then its match on the right.

Item
Match
Surface area & volume

3D solids: surface area & volume

AI expects volumes and surface areas of prisms, cylinders, cones, spheres and pyramids from the formula booklet — e.g. sphere V = 4⁄3 πr³, cone V = 1⁄3 πr²h.

Model real objects (silos, tanks, packaging) as combinations of these solids.

Quick check

Angle of elevation

?From 30 m away, the angle of elevation to the top of a tower is measured. Which ratio finds the tower's height h using tan?
Recap

The big ideas to take away

Right-angle trig: sin=O⁄H, cos=A⁄H, tan=O⁄A; Pythagoras a²+b²=c²

Sine rule: a⁄sinA = b⁄sinB — a side–angle pair plus one more

Cosine rule: c² = a²+b²−2ab cosC — two sides + included angle

Triangle area: ½ab sinC

Arc & sector (radians): ℓ = rθ ; area = ½r²θ

Voronoi: edges are perpendicular bisectors → nearest-site regions

You have worked through the whole topic. Press Finish to see your score.

🏆

Mini-lesson complete!

⭐⭐⭐

You have covered SL Geometry & Trigonometry for AI. 🎉

Your stars: 0 / 0

Next: test yourself in the Evaluate stage, then lock it in with Verify.

📣 Smashed it? Share your score

Challenge a mate to beat your stars, or show a parent how you got on.

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