Last updated on Oct 23, 2026

Angle Theorems (Leaving Cert Mathematics): Flashcards

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Angle Theorems

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Vertically opposite angles

Always equal

Adjacent angles at line intersection

Supplementary ( $180^circ$ )

Alternate angles (parallel lines)

Equal

Equal alternate angles mean lines are

Parallel

Sum of triangle's interior angles

$180^circ$

Triangle's exterior angle equals

Sum of two non-adjacent interior angles

Angle opposite to $45^circ$ (vertically opposite)

$45^circ$

Supplementary angle to $45^circ$ at intersection

$135^circ$

Alternate angle to $70^circ$ (parallel lines)

$70^circ$

Third angle: triangle with $50^circ$ , $60^circ$

$70^circ$

Exterior $120^circ$ , one interior $50^circ$ : other interior

$70^circ$

Explore Leaving Cert Mathematics Revision Notes by Topics

Fundamentals of Geometry

The Basics

Theorems

Explore Leaving Cert Mathematics Model Answers by Topics

Fundamentals of Geometry

The Basics

Theorems

Explore Leaving Cert Mathematics Quizzes by Topics

Fundamentals of Geometry

The Basics

Theorems

Explore Leaving Cert Mathematics Exam Questions by Topics

Fundamentals of Geometry

The Basics

Theorems

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