Glossary

Trigonometry – Key Terms & Definitions

Essential trigonometry vocabulary for IGCSE Mathematics (0580). Each term includes a clear definition and example to help you understand and remember key concepts.

sine

Core

Ratio of opposite to hypotenuse in a right triangle

Example

$\sin 30° = 0.5$

cosine

Core

Ratio of adjacent to hypotenuse

Example

$\cos 60° = 0.5$

tangent

Core

Ratio of opposite to adjacent

Example

$\tan 45° = 1$

hypotenuse

Core

Longest side of right triangle, opposite the right angle

Example

In a 3-4-5 triangle, 5 is the hypotenuse

opposite

Core

Side across from the angle being used

Example

Opposite to angle A

adjacent

Core

Side next to the angle being used, not the hypotenuse

Example

Adjacent to angle A

bearing

Core

Direction measured clockwise from north as a three-figure number

Example

045° means north-east

sine rule

Extended

$\dfrac{a}{\sin A} = \dfrac{b}{\sin B} \text{ for any triangle}$

Example

Used when you have a side-angle pair

cosine rule

Extended

$a^2 = b^2 + c^2 - 2bc \cos A$

Example

Used with SAS or SSS

angle of elevation

Core

Angle measured upward from horizontal

Example

Looking up at a building

angle of depression

Core

Angle measured downward from horizontal

Example

Looking down from a cliff

included angle

Extended

Angle between two known sides

Example

$The C in Area = \tfrac{1}{2}ab\sin C$

Pythagoras theorem

Core

$a^2 + b^2 = c^2 \text{ for right triangles}$

Example

$3^2 + 4^2 = 5^2$

right angle

Core

An angle of exactly 90°

Example

Corner of a rectangle

three-figure bearing

Core

Bearing written with 3 digits

Example

North is 000°, East is 090°

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Frequently Asked Questions

How many trigonometry terms do I need to know for IGCSE?

This glossary covers 15 key trigonometry terms. Focus on understanding definitions and being able to use each term in context during exams.

Are these terms for Core or Extended?

Terms are labelled as Core or Extended. Core students should focus on Core-labelled terms, while Extended students need to know all terms.

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