Prove that (\cos A+\sin A)(\cos 2A+\sin 2A)=\cos A+\sin 3A

Gregory Emery 2022-01-17 Answered
Prove that (cosA+sinA)(cos2A+sin2A)=cosA+sin3A
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Expert Answer

soanooooo40
Answered 2022-01-18 Author has 35 answers
Use following facts:
cosAsin2A+sinAcos2A=sin(A+2A)=sin3A
cosAcos2A+sinAsin2A=cos(2AA)=cosA
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