cos18°的值
\u5f0f\u5b50cos9\u00b0-sin9\u00b0/sin18\u00b0cos18\u00b0\u7684\u503c\u662f\uff1f(cos9\u00b0\uff0dsin9\u00b0)/(sin18\u00b0cos18\u00b0)
=[\u221a2cos(9\u00b0\uff0b45\u00b0)]/[(1/2)sin(2\u00d718\u00b0)]
=2\u221a2(cos54\u00b0)/(sin36\u00b0)
=2\u221a2cos54\u00b0/cos54\u00b0
=2\u221a2
\u89e3:
(cos18sin36)^2
=1/4*(1+cos36)(1-cos72)
=1/4*(1+cos36-cos72-cos36cos72)
=1/4*(1+cos36cos72)
=5/16
\u6545cos18sin36=(\u68395)/4.
你可以看看参考资料里的
sin18>0
所以-0.9舍去
不知你1/2怎么得到
但就算=1/2
则是sin30=1/2
不是sin18
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绛旓細cos18銈44'25''鈮坈os18.7403銈 鈮0.947
绛旓細0.96891銆俢os鍥涘垎涔嬩竴鏄凡鐭ヨ搴︿负18搴︼紝閭ｄ箞cos18搴鐨勫绾︿负0.96891锛岀敱浜庤搴︿负18搴︽槸涓涓浐瀹氱殑閲忥紝鎵浠ュ彲浠ュ埄鐢ㄤ笁瑙掑嚱鏁扮殑鍏紡杩涜绮剧‘鐨勮绠椼
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