1) Cos6αCos2α - Sin6αSin2α = Cos(6α + 2α) = Cos8α
2) Sin(- 15°)Cos75° + Cos15°Sin75° = Sin75°Cos15° - Sin15°Cos75° =
= Sin(75° - 15°) = Sin60° =√3/2
3)
4) Cos(α - β) - 2SinαSinβ = CosαCosβ + SinαSinβ - 2SinαSinβ =
= CosαCosβ - SinαSinβ = Cos(α + β)
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1) Cos6αCos2α - Sin6αSin2α = Cos(6α + 2α) = Cos8α
2) Sin(- 15°)Cos75° + Cos15°Sin75° = Sin75°Cos15° - Sin15°Cos75° =
= Sin(75° - 15°) = Sin60° =√3/2
3)
4) Cos(α - β) - 2SinαSinβ = CosαCosβ + SinαSinβ - 2SinαSinβ =
= CosαCosβ - SinαSinβ = Cos(α + β)
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