求证:(1),sin(a+β)sin(a-β)=sin^2a-sin^2β,(2),cos(a+β)cos(a-β)=cos^2a-sin^2β,(3),sin(a+β) cos(a-β)=sinacosa+sinβcosβ求证:1,角θ为第四象限角的充分必要条件是sinθ0 2,角θ为第二象限角的充分必要条件是cosθ
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![求证:(1),sin(a+β)sin(a-β)=sin^2a-sin^2β,(2),cos(a+β)cos(a-β)=cos^2a-sin^2β,(3),sin(a+β) cos(a-β)=sinacosa+sinβcosβ求证:1,角θ为第四象限角的充分必要条件是sinθ0 2,角θ为第二象限角的充分必要条件是cosθ](/uploads/image/z/665955-27-5.jpg?t=%E6%B1%82%E8%AF%81%EF%BC%9A%281%29%2Csin%28a%2B%CE%B2%29sin%28a-%CE%B2%29%3Dsin%5E2a-sin%5E2%CE%B2%2C%282%29%2Ccos%28a%2B%CE%B2%29cos%28a-%CE%B2%29%3Dcos%5E2a-sin%5E2%CE%B2%2C%283%29%2Csin%28a%2B%CE%B2%29+cos%28a-%CE%B2%29%3Dsinacosa%2Bsin%CE%B2cos%CE%B2%E6%B1%82%E8%AF%81%EF%BC%9A1%2C%E8%A7%92%CE%B8%E4%B8%BA%E7%AC%AC%E5%9B%9B%E8%B1%A1%E9%99%90%E8%A7%92%E7%9A%84%E5%85%85%E5%88%86%E5%BF%85%E8%A6%81%E6%9D%A1%E4%BB%B6%E6%98%AFsin%CE%B80+2%2C%E8%A7%92%CE%B8%E4%B8%BA%E7%AC%AC%E4%BA%8C%E8%B1%A1%E9%99%90%E8%A7%92%E7%9A%84%E5%85%85%E5%88%86%E5%BF%85%E8%A6%81%E6%9D%A1%E4%BB%B6%E6%98%AFcos%CE%B8)
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