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The value of sin — sin = + sin --sin+sin - sin
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Sin(8π/7) + Sin(4π/7) + Sin(2π/7)
= 2.Sin(6π/7).Cos(2π/7) + Sin(2π/7) [As Sin(A) + Sin(B) = 2.Sin((A+B)/2).Cos((A+B)/2)]
=2.Sin(6π/7).Cos(2π/7) + 2.Sin(π/7).Cos(π/7)
=2.Sin(π - 6π/7).Cos(2π/7) + 2.Sin(π/7).Cos(π/7) [As Sin(π - A) = Sin(A)]
=2.Sin(π/7).Cos(2π/7) + 2.Sin(π/7).Cos(π/7)
= 2.Sin(π/7).[Cos(2π/7) + Cos(π/7)]
= 2.Sin(π/7).[2.Cos(3π/14). Cos(π/14)]
plz mark it as brilliant
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