1.

सिद्ध कीजिए कि - `cos^(2)48^(@)-sin^(2)12^(@)=(sqrt5+1)/(8)`

Answer» बायाँ पक्ष `=cos^(2)48^(@)-sin^(2)12^(@)`
`=cos(48^(@)+12^(@))cos(48^(@)-12^(@))`
`" "[because cos^(2)A-sin^(2)B=cos(A+B)cos(A-B)]`
`=cos 60^(@)cos 36^(@)`
`=(1)/(2)((sqrt5+1))/(4)=(sqrt5+1)/(8)=` दायाँ पक्ष


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