23 Maths -- Trigonometry

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The Tangent Law

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From Sine Law,
→b = 2R sin B............(i)
→c = 2R sin C............(ii)
Subtracting eqⁿ (ii) from (i)
b - c = 2R(sin B - sin C)............(I)
Adding eqⁿ (i) and (ii)
b + c = 2R(sin B + sin C)............(II)
Dividing eqⁿ (I) and (II)

This verifies the Tangent Law, the remaining result follow similar process.

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