Show that in any , .

MATHEMATICS · Subjective · A Level · Mathematics · Trigonometry · Trigonometry

Problem

Show that in any △ABC\triangle ABC, a3cos⁡3B+3a2bcos⁡(2B−A)+3ab2cos⁡(B−2A)+b3cos⁡3A=c3a^3\cos3B+3a^2b\cos(2B-A)+3ab^2\cos(B-2A)+b^3\cos3A=c^3.

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