Detailed notes on Geometry and Trigonometry for Edexcel IGCSE Mathematics, covering key concepts, explanations, examples, and exam-focused revision points.
3D Shapes and Volume Study Notes — Edexcel IGCSE 4MA1 Higher Tier (2026 onwards)
Volumes and surface areas of cuboids, prisms, cylinders, pyramids, cones, spheres. Memorise the formulae.
At a glance
Cuboid: V=lwh.
Prism: V= cross-section area ×l.
Cylinder: V=πr2h.
Pyramid/cone: V=31× base × height.
Sphere: V=34πr3, SA=4πr2.
Cone curved surface: πrl (slant height).
Volume in cubes (cm3, m3).
What you’ll learn
Mapped to the Pearson Edexcel IGCSE 4MA1 syllabus (2026 onwards).
4.5 — Find surface areas (including formulae and net method).
4.5 — Use Pythagoras to find dimensions in 3D.
Prisms (including cuboids and cylinders)
V= cross-section area × length. Uniform along length.
Prism = uniform cross-section.
General formula: V= area of cross-section ×l.
Specific:
Shape
Volume
Cube
s3
Cuboid
lwh
Triangular prism
21bh△×l
Cylinder
πr2h
Surface area of cylinder: 2 circles + curved (rectangle when unrolled).
SAcylinder=2πr2+2πrh.
The curved surface unrolls to a rectangle: width = circumference 2πr, height = h.
Worked qualitative. Why is the curved surface of a cylinder a rectangle?
Imagine cutting and unrolling.
Width: circumference 2πr.
Height: h.
Area: 2πr×h=2πrh.
Edexcel tip. Always state UNITS for volume (cm³, m³). Mark schemes deduct for using cm².
V= cross-section × length.
Cuboid: lwh.
Cylinder: πr2h.
Cylinder SA: 2πr2+2πrh.
Pyramids and cones
V=31× base × height. Cone curved surface uses slant.
Pyramid volume: V=31× base area ×h.
The 31 is universal for pyramids/cones — exactly 31 of the bounding prism/cylinder.
Cone-specific:
Vcone=31πr2h
SAcone=πr2+πrl
where h = perpendicular height, l = SLANT height.
h,r,l form a right triangle:h2+r2=l2 (Pythagoras).
Perpendicular height h, radius r and slant height l form a right triangle.
Worked example. Cone with r=5, l=13.
Find h: h2=169−25=144, h=12.
V=31π×25×12=100π.
Curved surface: π×5×13=65π.
Total SA: 25π+65π=90π.
Worked qualitative. Why is cone volume 31 of cylinder volume (same r,h)?
Cylinder: πr2h.
Cone fits inside it.
Calculus shows the cone is exactly 31.
Geometrically: cones with the same base and apex tapered uniformly.
Edexcel tip. Pyramids/cones use PERPENDICULAR height for VOLUME, SLANT height for CURVED SURFACE. Don't confuse.
V=31× base × height.
Cone: 31πr2h.
Curved surface: πrl.
Use Pythagoras for h,r,l.
Spheres
V=34πr3, SA=4πr2.
Sphere formulas:
V=34πr3SA=4πr2
Both use the radius r.
A hemisphere is exactly half a sphere; its surface adds a flat circular base.
Hemisphere (half a sphere):
Vhemi=32πr3.
SAhemi=2πr2 (curved) plus πr2 (circular base) = 3πr2.
Worked example. Sphere with r=6.
Volume: 34π×216=288π cm³.
Surface: 4π×36=144π cm².
Worked qualitative. Why is sphere SA 4πr2, exactly 4× area of equator circle?
Beautiful result from calculus.
Beyond IGCSE proof — but memorise.
Edexcel tip. When the question says 'in terms of π', leave answer as 288π, not the decimal.
V=34πr3.
SA=4πr2.
Hemisphere: half + circular base.
Both use r.
3D Pythagoras
Used for finding diagonals of cuboids and other 3D distances.
3D Pythagoras for the long diagonal of a cuboid:
If a cuboid has sides a,b,c, the long diagonal d satisfies:
d2=a2+b2+c2
Why? First, the floor diagonal: dfloor2=a2+b2 (2D Pythagoras).
Then, considering the long diagonal as the hypotenuse of a right triangle with sides dfloor and c (height):
d2=dfloor2+c2=a2+b2+c2.
Pythagoras twice: first the floor diagonal, then combine with height c.
Worked example. Cuboid 3×4×12. Long diagonal?
d2=9+16+144=169.
d=13.
Worked qualitative. What's the diagonal of a unit cube (1×1×1)?
d2=1+1+1=3.
d=3≈1.732.
Edexcel tip. 3D Pythagoras applies wherever you can find a right triangle in 3D. Often combined with cones or other shapes.
d2=a2+b2+c2 for cuboid diagonal.
Apply 2D Pythagoras twice.
Find right triangles within the 3D shape.
Common in cone problems too (h,r,l).
Quick recap
Prisms: V= cross-section × length.
Pyramids/cones: V=31× base × height.
Sphere: V=34πr3, SA=4πr2.
Cone curved surface: πrl (slant).
3D Pythagoras: d2=a2+b2+c2.
Memorise this
Verbatim phrases and definitions Edexcel mark schemes credit.
Cuboid: V=lwh.
Cylinder: V=πr2h.
Pyramid/cone: V=31× base × height.
Sphere: V=34πr3, SA=4πr2.
Cone curved surface: πrl.
How it’s examined
3D shapes appear every Higher Tier paper (5-8 marks). Often combined with Pythagoras or scale factors. Examiner reports flag (1) using slant for volume, (2) forgetting 31 for pyramids/cones, (3) wrong units (cm² vs cm³).
(c) Surface: base circle πr2=25π. Curved: πrl=5×13×π=65π.
Step 4
Total: 25π+65π=90π cm².
Answer
(a) h=12 cm (b) V=100π (c) SA =90π cm²
Examiner tip
Cone volume uses PERPENDICULAR height. Curved surface uses SLANT height. Edexcel mark schemes are precise about this.
4Sphere
Higher• Adapted from 4MA1/2H Jan 2024 Q14• sphere
▼
Question
Sphere of radius 6 cm. Find (a) volume, (b) surface area. In terms of π.
Step-by-step solution
Step 1
(a) V=34πr3=34π×216=288π cm³.
Step 2
(b) SA=4πr2=4π×36=144π cm².
Answer
(a) V=288π (b) SA =144π cm²
5Prism volume
Foundation• prism
▼
Question
Triangular prism: triangle base 6 cm × height 4 cm; prism length 10 cm. Volume?
Step-by-step solution
Step 1
Cross-sectional area (triangle): 21×6×4=12 cm².
Step 2
Volume = cross-section × length: 12×10=120 cm³.
Answer
120 cm³
Key Formulae — 3D Shapes and Volume
The formulae you need to memorise for 3d shapes and volume on the Pearson Edexcel IGCSE 4MA1 paper, with every variable defined in plain English and a note on when to use it.
Cuboid volume
V=lwh
l,w,h
length, width, height
When to use
Cuboids and cubes.
Example
5×3×4=60.
Prism volume
V=Across-section×l
Across-section
area of the cross-section
l
length of prism
When to use
Any prism (uniform cross-section). Includes cuboids.
Example
Triangle base area 12, length 10: V=120.
Cylinder
V=πr2h,SA=2πr2+2πrh
r
radius
h
height
When to use
Cylinders. SA = 2 circles + curved surface.
Example
r=4,h=10: V=160π, SA=112π.
Pyramid volume
V=31×base area×h
h
perpendicular height
When to use
Pyramids (square, triangular, any base).
Example
Square base area 16, height 9: V=31×16×9=48.
Cone
V=31πr2h,SA=πr2+πrl
r
radius
h
perpendicular height
l
slant height
When to use
Cones. Curved surface uses SLANT height.
Example
r=5,h=12: V=100π. l=13: SAcurve=65π.
Sphere
V=34πr3,SA=4πr2
r
radius
When to use
Spheres.
Example
r=6: V=288π, SA=144π.
Key Definitions and Keywords — 3D Shapes and Volume
Definitions to memorise and the exact keywords mark schemes credit for 3d shapes and volume answers — sharpened from recent examiner reports for the 2026 Pearson Edexcel IGCSE 4MA1 sitting.
Prism
Examiner keyword
A 3D shape with a UNIFORM cross-section throughout its length.
A 3D shape with a polygon base, sides meeting at a single apex.
Slant height vs perpendicular height (cone/pyramid)
Slant: along the surface. Perpendicular: 90° from base to apex. Related by Pythagoras.
Common Mistakes and Misconceptions — 3D Shapes and Volume
The traps other students keep falling into on 3d shapes and volume questions — taken from recent Pearson Edexcel IGCSE 4MA1 examiner reports and mark schemes — and how to avoid them.
✕Using slant instead of perpendicular height for volume