sin²1°+sin²2°+sin²3°+...+sin²88°+sin²89°+sin²90°=
等于多少?
人气：256 ℃ 时间：2020-07-05 15:59:23
解答
sin21°+sin22°+sin23°+...+sin288°+sin289°+sin290°sin21°+sin22°+sin23°+..+sin244°+sin245°+cos244°+cos243°+...+cos21°+sin290°.根据sin2a+cos2a=1,上式得到=1+1+..+1/2+ 1=45.5
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