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secondary 3 | A Maths

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Cosine rule :

① c² = a² + b² - 2ab cos ∠C

Or

② cos ∠C = (a² + b² - c²) / 2ab

Then 180° - ∠A - ∠B = ∠C (Angle sum of triangle)

You can just take a to be 2 units, b to be 3 units and c to be 4 units.

Alternatively,

Use variant ② of cosine rule :

② cos ∠C = (a² + b² - c²) / 2ab

then ∠C = cos-¹ [(a² + b² - c²) / 2ab]

sin ∠C = sin (cos-¹ [(a² + b² - c²) / 2ab])

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*done*{{ upvoteCount }} Upvotes

*clear*{{ downvoteCount * -1 }} Downvotes

He just wrote 'sin' by accident instead of 'cos'