सिद्ध कीजिए कि –
`sin.(pi)/(10)+sin.(13pi)/(10)=-(1)/(2)`
`sin.(pi)/(10)+sin.(13pi)/(10)=-(1)/(2)`
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बायाँ पक्ष `=sin.(pi)/(10)+sin.(13pi)/(10)`
`=sin.(pi)/(10)+sin.(pi+(3pi)/(10))=sin.(pi)/(10)-sin.(3pi)/(10)`
`=sin 18^(@)-sin 54^(@)`
`=sin 18^(@)-sin(90^(@)-36^(@))`
`=sin 18^(@)-cos 36^(@)=(sqrt5-1)/(4)-(sqrt5+1)/(4)=-(1)/(2)=` दायाँ पक्ष