(sin10°+sin50°)/sin35°·sin55° =? 具体过程. 尽快,谢谢.
来源:学生作业帮 编辑:拍题作业网作业帮 分类:数学作业 时间:2024/04/25 07:46:28
(sin10°+sin50°)/sin35°·sin55° =? 具体过程. 尽快,谢谢.
(sin10°+sin50°)/(sin35°·sin55°)
(sin10°+sin50°)/(sin35°·sin55°)
根据和差化积公式sinα+sinβ=2sin[(α+β)/2]·cos[(α-β)/2]
sin10°+sin50°=2sin[(10°+50°)/2]·cos[(10°-50°)/2]=2sin30°·cos(-20°)=cos20°
根据积化和差公式sinαsinβ= -[cos(α+β)-cos(α-β)]/2
sin35°·sin55°= -[cos(35°+55°)-cos(35°-55°)]/2= (cos20°-cos90°)/2= cos20°/2
∴(sin10°+sin50°)/(sin35°·sin55°)=cos20°/(cos20°/2)=2
sin10°+sin50°=2sin[(10°+50°)/2]·cos[(10°-50°)/2]=2sin30°·cos(-20°)=cos20°
根据积化和差公式sinαsinβ= -[cos(α+β)-cos(α-β)]/2
sin35°·sin55°= -[cos(35°+55°)-cos(35°-55°)]/2= (cos20°-cos90°)/2= cos20°/2
∴(sin10°+sin50°)/(sin35°·sin55°)=cos20°/(cos20°/2)=2
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