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11TH · MATH

Question 5

menu_bookSolutionmenu_bookTheorymenu_book•(i)cos⁡20∘cos⁡40∘cos⁡60∘cos⁡80∘=116\cos 20^\circ \cos 40^\circ \cos 60^\circ \cos 80^\circ = \dfrac{1}{16}cos20∘cos40∘cos60∘cos80∘=161​menu_book•(ii)sin⁡π9sin⁡2π9sin⁡π3sin⁡4π9=316\sin\dfrac{\pi}{9}\sin\dfrac{2\pi}{9}\sin\dfrac{\pi}{3}\sin\dfrac{4\pi}{9} = \dfrac{3}{16}sin9π​sin92π​sin3π​sin94π​=163​menu_book•(iii)sin⁡10∘sin⁡30∘sin⁡50∘sin⁡70∘=116\sin 10^\circ \sin 30^\circ \sin 50^\circ \sin 70^\circ = \dfrac{1}{16}sin10∘sin30∘sin50∘sin70∘=161​
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school

11TH · MATH

Question 5

menu_bookSolutionmenu_bookTheorymenu_book•(i)cos⁡20∘cos⁡40∘cos⁡60∘cos⁡80∘=116\cos 20^\circ \cos 40^\circ \cos 60^\circ \cos 80^\circ = \dfrac{1}{16}cos20∘cos40∘cos60∘cos80∘=161​menu_book•(ii)sin⁡π9sin⁡2π9sin⁡π3sin⁡4π9=316\sin\dfrac{\pi}{9}\sin\dfrac{2\pi}{9}\sin\dfrac{\pi}{3}\sin\dfrac{4\pi}{9} = \dfrac{3}{16}sin9π​sin92π​sin3π​sin94π​=163​menu_book•(iii)sin⁡10∘sin⁡30∘sin⁡50∘sin⁡70∘=116\sin 10^\circ \sin 30^\circ \sin 50^\circ \sin 70^\circ = \dfrac{1}{16}sin10∘sin30∘sin50∘sin70∘=161​
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