已知sinα+cosα=4/5,则sin2α=
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已知sinα+cosα=4/5,则sin2α=
sinα+cosα=4/5,
平方得
1+2sinαcosα=16/25
则sin2α=-9/25
再问: sin65°+sin15°sin10°/sin25°-cos25°cos80°= log2为底cosπ/9+log2为底cos2π/9+log2为底cos4π/9=
再答: 问我这么多,好。 疑似错了。已经修正 sin65°+sin15°sin10°/sin25°-cos15°cos80° =(sin(75°-10°)+cos75°sin10°)/(cos65°-cos15°cos80°) =sin75°cos10°/sin15°sin80° =tan75°=tan(45°+30°)=2+根号3 log2为底cosπ/9+log2为底cos2π/9+log2为底cos4π/9 =log2为底(cosπ/9cos2π/9cos4π/9) 因为cosπ/9cos2π/9cos4π/9 =(sinπ/9cosπ/9cos2π/9cos4π/9)/sinπ/9 =(sin8π/9)/(8sinπ/9) =1/8 所以原式=-3
平方得
1+2sinαcosα=16/25
则sin2α=-9/25
再问: sin65°+sin15°sin10°/sin25°-cos25°cos80°= log2为底cosπ/9+log2为底cos2π/9+log2为底cos4π/9=
再答: 问我这么多,好。 疑似错了。已经修正 sin65°+sin15°sin10°/sin25°-cos15°cos80° =(sin(75°-10°)+cos75°sin10°)/(cos65°-cos15°cos80°) =sin75°cos10°/sin15°sin80° =tan75°=tan(45°+30°)=2+根号3 log2为底cosπ/9+log2为底cos2π/9+log2为底cos4π/9 =log2为底(cosπ/9cos2π/9cos4π/9) 因为cosπ/9cos2π/9cos4π/9 =(sinπ/9cosπ/9cos2π/9cos4π/9)/sinπ/9 =(sin8π/9)/(8sinπ/9) =1/8 所以原式=-3
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