Question

सिद्ध कीजिए कि
`4(cos^(3)10^(@)+sin^(3)20^(@))=3(cos10^(@)+sin 20^(@))`

Answer 1

बायाँ पक्ष `=4(cos^(3)10^(@)+sin^(3)20^(@))=4[(1)/(4)(cos3xx10^(@)+3cos10^(@))xx(1)/(4)(3sin 20^(@)-sin 3xx20^(@))]`
`=4xx(1)/(4){cos 10^(@)+3cos10^(@)+3sin 20^(@)-sin 60^(@)}`
`=(sqrt3)/(2)+3cos10^(@)+3sin 20^(@)-(sqrt3)/(2)=3cos 10^(@)+3sin 20^(@) = ` दायाँ पक्ष