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Sine Rule and Cosine Rule
Chapter summary, hard words and model exam answers for ICSE Class 10 Hindi.
Free online summary and notes (ICSE Class 10 Hindi). Read it here, no PDF download needed.
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Mathematics · CBSE 10 · ICSE 10 · GCSE (AQA, Edexcel, OCR)
Summary
Label the corners A, B, C and the opposite sides a, b, c. Both rules depend on this matching, so always label first.
Use it when you can pair a side with its opposite angle. Flip it to sin A / a = sin B / b = sin C / c when you are finding an angle.
Rearranged to find an angle: cos A = (b² + c² − a²) / 2bc. Pythagoras is just the cosine rule with A = 90°.
Draw the triangle and mark what you know. The pattern of the marks tells you the rule before you do any algebra.
Hard words & meanings
| sine rule | the relation a / sin A = b / sin B = c / sin C for any triangle |
| cosine rule | a² = b² + c² − 2bc cos A, linking three sides and one angle |
| included angle | the angle that sits between two given sides |
| opposite side | the side that faces a particular angle across the triangle |
| SAS | data given as two Sides and the Angle between them |
| SSS | data given as all three Sides |
| ambiguous case | an SSA situation where two different triangles can fit the data |
| bearing | a direction measured clockwise from north, written as three digits |
Model exam answers, grammar & audio
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