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Tangent - GCSE Maths Definition

Reviewed by: Dan Finlay

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The word tangent has different (but ultimately related) meanings in mathematics.

In GCSE Mathematics, the tangent function is one of the three basic trigonometric ratios. It can be used to find missing sides and angles in right-angled triangles. Specifically, if the angle in the triangle we are working with is called theta, then the tangent value of theta is found by dividing the length of the side opposite theta, by the length of the adjacent side.

As an equation, we would write this as

tan space theta equals fraction numerator o p p o s i t e over denominator a d j a c e n t end fraction

You may remember this as the TOA part of the acronym SOHCAHTOA.

Also, a tangent is a straight line that intersects a curve at exactly one point (i.e. it does not cross the curve). Tangent lines are used to find or estimate the gradients of curves, and in circle theorems, a tangent (line) and a radius (or diameter) meet perpendicularly (i.e. at 90°).

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Dan Finlay

Reviewer: Dan Finlay

Expertise: Maths Subject Lead

Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.

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