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In triangle ABC, which expression gives c² by the cosine rule?
Aa² + b² − 2ab sin C
Ba² − b² − 2ab cos C
Ca² + b² − 2ab cos C
Da² + b² + 2ab cos C
Answer & Solution
Correct answer: C. a² + b² − 2ab cos C
The cosine rule subtracts twice the product of the two sides and the cosine of the included angle.
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