Integrate:
$$\int\frac{\cos5x+\cos4x}{1-2\cos 3x}\; dx$$
I tried using sums and products formula but couldn't make it. How to approach this problem?
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2Whatever you try ,you should add your try with question.. – Aakash Kumar Aug 18 '16 at 12:24
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Hint. By using De Moivre's formula $$ e^{ix}=\cos x+i \sin x $$ one may prove that $$ \frac{\cos 5x+\cos 4x}{1-2\cos 3x} =-\cos x-\cos (2x) $$ then the integral is easier to evalute.
Olivier Oloa
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Hint: $$\cos x =\frac {e^{ix} + e^{-ix}}{2} $$ Or
Multiply and divide by $\sin \left (\frac {3x}{2}\right )$
Aakash Kumar
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