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Sum of angles in a triangle worksheet (with solutions)

Sum of angles in a triangle worksheet (with solutions)

Subject: Mathematics

Age range: 11-14

Resource type: Worksheet/Activity

Last updated

11 August 2026

pdf, 130.41 KB
pdf, 130.41 KB

A worksheet on evaluating the third angle in a triangle given the other two using the fact that their sum is 180 degrees. Solutions are included.

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A bundle is a package of resources grouped together to teach a particular topic, or a series of lessons, in one place.

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Angle Relationships, Parallel Lines & Triangles Geometry Bundle | GCSE 9-1

A collection of 6 worksheets on angles, lines and triangles based on the GCSE 9-1 specification. The following worksheets are included: * Types of angles * Complementary, supplementary and opposite angles * Angles in parallel lines * Sum of angles in a triangle * Exterior Angles of a Triangle * Isosceles, Equilateral and Right-Angled Triangles Detailed solutions are included. Master angle facts and triangle properties with this complete geometry worksheet bundle! Perfectly optimized for KS3 and GCSE 9-1 math revision (Foundation and Higher), this print-and-go pack covers parallel lines, angle types, and multi-step equations with full step-by-step worked solutions. ________________________________________ Looking for a rigorous, print-and-go resource to help your students master angle rules and geometric reasoning? This GCSE 9-1 Angles, Lines and Triangles Worksheet Bundle contains highly structured practice sheets designed to build fluency and algebraic confidence. Moving from basic angle classification to multi-step exam-style equations, this bundle is perfect for formal lessons, independent revision, homework packs, cover work, or intervention groups! Every page includes an uncrowded, student-friendly layout and comes paired with a complete, step-by-step worked solution key showing the exact algebraic workings to solve for \(x\). ________________________________________ **What's Included in This Bundle?** • **Types of Angles & Triangles:** Identification mastery for acute, obtuse, right, straight, and reflex angles, alongside scalene, isosceles, and equilateral properties. • **Complementary, Supplementary & Vertically Opposite Angles:** Multi-step algebraic equations requiring students to set up expressions that add up to 90 or 180 degrees. • **Angles in Parallel Lines:** Clear diagrams focusing on alternate, corresponding, and co-interior/allied angle theorems (using formal geometric reasons). • **Interior & Exterior Angles of Triangles:** Comprehensive practice applying the triangle angle sum theorem (180 degrees) and the exterior angle theorem. ________________________________________ **Perfect For:** • KS3 Maths: Building a strong foundational mastery of basic angle facts and algebraic manipulation. • KS4 / GCSE 9-1 Prep: targeted revision for both Foundation and Higher tier students aiming for maximum marks on geometry questions. • Cover Lessons & Homework: Structured, self-explanatory layout that requires zero preparation from you or a cover teacher. ________________________________________

£4.95
Bundle

Interior and Exterior Angles in Triangles & Polygons Geometry Worksheets

A collection of three worksheets on the following topics: * Sum of angles in a triangle: a worksheet on evaluating the third angle in a triangle given the other two using the fact that their sum is 180 degrees * Exterior Angles of a Triangle: a worksheet on the exterior angles of a triangle. The exercises require to use the fact that an exterior angle of a triangle is equal to the sum of the two interior opposite angles. * Interior and exterior angles in regular polygons: a worksheet on calculate the interior and exterior angle sum of regular polygons and the measure of each interior and each exterior angle of regular polygons. Detailed solutions are provided. Master interior and exterior angles with this comprehensive, ready-to-print geometry maths worksheet bundle! Perfect for KS3, KS4, and GCSE Maths classrooms, this 3-resource collection includes fully worked step-by-step solutions to save you valuable marking time. ________________________________________ Help your secondary maths students conquer geometric properties with this no-prep angles in triangles and polygons worksheet bundle! This collection features three carefully scaffolded, rigorous resources designed to take students from foundational angle rules to advanced multi-step geometric problem-solving. Whether you need targeted homework assignments, no-prep cover plans, extension tasks, or comprehensive exam revision, these printable activities provide clear, structured practice that fits seamlessly into any secondary school maths curriculum. **What’s Included in This Bundle?** This cost-saving bundle contains three complete worksheets, each including its own detailed, step-by-step fully worked solutions: **1. Sum of Angles in a Triangle Worksheet** o 10 multi-step problems calculating missing interior angles. o Promotes algebraic setup to find unknown variables. **2. Exterior Angle Theorem Worksheet** o 6 scaffolded questions applying the exterior angle rule. o Includes challenging application problems involving isosceles and equilateral triangles. **3. Interior and Exterior Angles in Regular Polygons Worksheet** o 13 advanced questions focusing on regular polygon properties. o Covers finding interior angle sums, individual interior/exterior angles, and determining the number of sides of polygons (ranging from pentagons to 36-gons). **Core Skills Covered:** • Applying the triangle angle sum rule (interior angles add up to 180 degrees). • Utilizing the exterior angle theorem to solve geometric diagrams. • Working with angles on a straight line and supplementary linear pairs. • Calculating interior and exterior angle measures for various regular polygons using standard geometric formulas. • Formulating and solving multi-step algebraic equations based on visual geometric properties. **Perfect For:** • Key Stage 3 (KS3) Math Classes (Years 7–9) • Key Stage 4 (KS4) & GCSE Foundation and Higher Tiers • IGCSE & International Baccalaureate (IB) Maths Prep • Homework, Classwork, Cover Work, or Exam Revision **Exam Board Alignment:** • Excellent preparation for Edexcel, AQA, OCR, and Cambridge International (CIE) specifications covering properties of polygons, angles, and geometric reasoning. ________________________________________

£2.90
Bundle

Complementary Supplementary Vertical & Triangle Angles Worksheets

A collection of three worksheets. Two worksheets on identifying complementary, supplementary and vertically opposite angles and using their properties to find the value of a variable. One worksheet on evaluating the third angle in a triangle given the other two using the fact that their sum is 180 degrees. Detailed solutions are included. Master angle facts and the angles in a triangle rule with this no-prep maths resource bundle! Perfect for KS3 (Year 8 and Year 9). Students apply algebra to form and solve multi-step linear equations for x. Includes full step-by-step answers keys! The ultimate no-prep bundle for mastering angle facts, triangles, and geometric equations! This comprehensive worksheet package is perfectly tailored for secondary maths classrooms. It beautifully bridges the gap between geometry rules and algebraic problem-solving, taking students from basic angle tracking to advanced multi-step equation solving. **What's Included in This Bundle:** **Unit 1: Complementary, Supplementary, & Vertically Opposite Angles** • Concept Mastery Table: Practice calculating complements and supplements for given values. • Geometric Diagrams: Solve for x using intersecting lines, right angles, and straight lines. • Algebraic Word Problems: Challenging worded scenarios requiring algebraic setup and calculation. • Detailed Solution Keys: Full, step-by-step mathematical breakdowns for every single problem. **Unit 2: Sum of Angles in a Triangle** • Visual Triangle Practice: Solve for the missing interior angle x inside a wide variety of triangle types. • Step-by-Step Answer Keys: Clear, complete solutions included for easy marking or self-checking. **Key Benefits for Your Classroom:** • **Print and Go:** Zero prep work required—simply download, print, and copy! • **Scaffolded Learning:** Tasks build naturally from basic numeric rules to multi-step linear equations. • **Self-Checking Friendly:** Detailed answer sheets make independent marking or peer-assessment easy. • **Versatile Use:** Ideal for main lessons, homework, revision, or cover work. **Curriculum Alignment (UK National Curriculum):** • KS3 Geometry: Apply angle facts to solve increasingly complex problems. • KS3 Geometry: Understand and use the sum of angles in a triangle, vertically opposite angles, and angles on a straight line. • KS3 Algebra: Form and solve multi-step linear equations with one variable. ________________________________________

£2.90
Bundle

Triangles (sum of angles-inequalities-isosceles) Bundle

A collection of three worksheets on the following topics: * Sum of angles in a triangle: evaluating the third angle in a triangle given the other two using the fact that their sum is 180 degrees * Triangle inequalities: deciding whether three numbers can represent the lengths of the sides of a triangle and determining the possible lengths of the third side of a triangle given the lengths of the other two sides * Isosceles triangles: deciding whether a given triangle is an isosceles triangle using the properties of isosceles triangles( two equal sides, two equal angles, any two of the median, bisector and height corresponding to the same side coincide). Detailed solutions are included.

£2.90
Bundle

GCSE Maths-Geometry Revision Pack

A bundle of 10 worksheets (with detailed solutions) on Geometry topics appropriate for GCSE students. Each worksheet contains questions for students of various abilities. The topics covered by these worksheets include: * Angles in parallel lines * Complementary, supplementary and opposite angles * Sum of angles in a triangle * Interior and exterior angles in regular polygons * Units of measurement for area and volume * Area of trapezium * Circumference and area of a circle * Area and volume of a sphere * Volume and surface area of a cone * Density The pack is ideal for use in revision sessions or for individual study. The solutions provided are very clear and explanatory.

£7.90
Bundle

Angles in a triangle-Angles in parallel lines Worksheets (with solutions)

A collection of three worksheets on each of the following topics: * Angles in a triangle * Angles in parallel lines * Complementary, supplementary and opposite angles Solutions are included.

£2.80

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