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GR.7.2

Similar triangles and trigonometric ratios

Understand the link between similar triangles and the trigonometric ratios

3 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 5–8 Core 🇺🇸 US

Similarity to define sine, cosine, and tangent | Basic trigonometry | Trigonometry | Khan Academy

Khan Academy 459K views

Shows exactly why similar triangles make sin, cos and tan constant for an angle.

Grade 4–7 Core 🇬🇧 UK

Similar Triangles - GCSE Maths

1st Class Maths 356K views

Clear UK GCSE walkthrough of finding missing lengths in similar triangles.

Jump to 0:10Important properties of similar triangles 2:40Example 1 - Connected triangles in parallel lines 5:34Example 2 - Connected triangles in parallel lines 7:51Example 3 - Overlapping triangles in parallel lines 11:42Example 4 - Overlapping triangles in parallel lines 13:10Example 5 - With ratios

Grade 4–6 Core 🇬🇧 UK

Trigonometry | SOH CAH TOA | Sin, Cos, Tan

Cognito 509K views

Neat UK intro to sin, cos and tan using SOH CAH TOA on right-angled triangles.

Jump to 0:00Intro & Identifying Right-Angled Triangles 0:28Labelling Sides 1:37Introduction to Trigonometric Ratios (Sin, Cos, Tan)2:05Using SOH CAH TOA 3:11Example 1: Finding an Unknown Angle 5:57Example 2: Finding an Unknown Side