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数学
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已知tan(π/4+a)=1/2
求cos2a/sin2a+cos²a
人气:117 ℃ 时间:2020-05-08 20:55:38
解答
tanπ/4=1所以(1+tana)/(1-tana)=1/22+2tana=1-tanatana=-1/3sina/cosa=tana=-1/3cosa=-3sina则cos²a=9sin²a因为sin²a+cos²a=1所以sin²a=1/10,cos²a=9/10cos2a=cos²a-sin²a...
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