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GR.12.1

Interior angles of triangles and quadrilaterals

Derive the sum of interior angles in triangles and quadrilaterals

5 hand-picked video lessons for this topic, each checked for relevance and clarity, graded by difficulty and labelled by depth. Press play to watch — nothing loads from YouTube until you do.

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Grade 3–6 Core 🇬🇧 UK

Angles in Triangles and Quadrilaterals | Grade 5 Crossover | GCSE Maths Tutor

The GCSE Maths Tutor 48K views

UK GCSE tutor covers angles in triangles then quadrilaterals, then combining shapes, with practice.

Jump to 0:34Angles in Triangles 5:53Practice Questions 9:09Angles in Quadrilaterals 10:54Practice Questions 12:55Combining Shapes 16:04Practice Question

Grade 2–5 Core 🇬🇧 UK

Angles in a Quadrilateral

corbettmaths 328K views

Corbettmaths clearly finds missing angles in quadrilaterals, including special shapes like kites and trapezia.

Grade 2–5 Core 🇬🇧 UK

GCSE Maths - 5 Angle Rules to Know (2026/27 exams)

Cognito 258K views

Cognito walks through the key angle rules, including triangle 180 and quadrilateral 360 sums.

Jump to 0:14Rule 1: Angles in a Triangle 2:02Rule 3: Angles in a Quadrilateral 3:09Rule 5: Isosceles Triangles 5:18Complex Problem Example

Grade 2–4 Recap 🇬🇧 UK

Interior and Exterior Angles triangles and quadrilaterals

Will Gray - Harold M Brathwaite SS (2482) 108 views

Corbettmaths clearly explains the 180 rule and finding missing angles in scalene, right and isosceles triangles.

Grade 2–4 Recap 🇺🇸 US

Finding the Missing Angle of a Quadrilateral | Math with Mr. J

Math with Mr. J 284K views

Short, clear walkthrough of finding a missing angle in a quadrilateral using the 360 sum.