Q 5f no 6
If Sin Ø + Sin 2Ø = a, & Cos Ø + Cos 2Ø = b Prove that (a2 + b2) (a2 + b2-3) =2 b
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Sin Ø + Sin 2Ø = a Let c = Ø+2Ø = 3Ø and d = Ø-2Ø = -Ø c + d = 2Ø c - d = 4Ø
Therefore a = 2 Sin Ø. Cos 2Ø & a2 = 4 Sin2 Ø. Cos22 Ø | Cos Ø + Cos 2Ø = b Let c = Ø+2Ø = 3Ø and d = Ø-2Ø = -Ø c + d = 2Ø c - d = 4Ø
Therefore b = 2 Cos Ø. Cos 2Ø & b2 = 4 Cos2 Ø. Cos22 Ø
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a2 + b2 = 4 Sin2 Ø. Cos22 Ø + 4 Cos2 Ø. Cos22 Ø = 4 Cos22 Ø (Sin2 Ø + Cos2 Ø) = 4 Cos22 Ø | |
Therefore (a2 + b2) (a2 + b2-3) = 4 Cos22Ø (4 Cos22 Ø-3) = 16 Cos4 2Ø – 12 Cos2 2Ø =4 Cos2Ø (4Cos32Ø – 3Cos 2Ø) =4 Cos 2Ø. Cos 6Ø
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2b = 4 Cos Ø. Cos 2Ø | |
Conclusion: 4 Cos Ø. Cos 2Ø = 4 Cos 2Ø. Cos 6Ø
CosØ = Cos 6Ø (??????)
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