使得cosk°=（sin99°+cos99°）/（sin99°-cos99°）成立的最小正整数k的值是
\u6c42\u89e3\u4e00\u9053\u6570\u5b66\u9898\uff1a\u4f7f\u5f97cosk\u00b0=\uff08sin99\u00b0+cos99\u00b0\uff09/\uff08sin99\u00b0-cos99\u00b0\uff09\u6210\u7acb\u7684\u6700\u5c0f\u6b63\u6574\u6570k\u7684\u503c\u662f________\u9996\u5148\u8981\u77e5\u9053cos2x=(cosx)^2-(sinx)^2=2(cosx)^2-1=1-2(sinx)^2,\u7136\u540e\u95ee\u9898\u5c31\u8fce\u5203\u800c\u89e3\u4e86\uff0ccosk=(sinx)^2-(cosx)^2=-cos198=cos18,\u6240\u4ee5k=18
\u539f\u5f0f\uff1dcos(36'+99')\uff1dcos135'\uff1d\uff0d\u221a2/2
**\u697c\u4e0a\u7684\u662f\u6765\u6363\u4e71\u7684\uff1f**
(sin99+cos99)/(sin99-cos99)=根号2(sin99cos45+sin45cos99)/根号2(sin99cos45-sin45cos99)
=sin(99+45)/sin(99-45)=sin144/sin54=sin36/cos36=tan36
题目应该是使得tank=(sin99+cos99)/(sin99-cos99)成立的最小正整数吧
k=36
如果是cos的话,k≈43.4,不是整数
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