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The value of `sin 78^@ - sin 66^@ - sin 42^@ + sin 6^@` is

Answer» The expression `=(sin78^(@)-sin42^(@))-(sin66^(@)-sin6^(@))=2cos(60^(@))sin(18^(@))-2cos36^(@).sin30^(@)`
`=sin18^(@)-cos36^(@)=(sqrt(5)-1)/(4) -(sqrt(5)+1)/(4)=-1/2`


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