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It is given that A is an obtuse angle and cosA=-sqrt5/3.

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Without using calculator,find the value of cos 3A


asked Jul 14, 2013 in TRIGONOMETRY by anonymous Pupil

1 Answer

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Using formula cos3A=4cos^3A-3cosA

Substitute -sqrt5/3 for cos A





answered Jul 14, 2013 by bradely Scholar