cos18度是多少 sin18度等于多少怎么计算？谢谢
cos18\u5ea6\u7b49\u4e8e\u591a\u5c11
\u8ba1\u7b97\u5668\u8ba1\u7b97\u7684\u7ed3\u679c
\u89e3\u6cd51.\u4ee4x = 18\u00b0
\u2234cos3x = sin2x
\u22344(cosx)^3 - 3cosx = 2sinxcosx
\u2235cosx\u2260 0
\u22344(cosx)^2 - 3 = 2sinx
\u22344sinx2 + 2sinx - 1 = 0,
\u53c80 < sinx < 1
\u2234sinx = (\u221a5 - 1)/4
\u5373sin18\u00b0 = (\u221a5 - 1)/4.
\u89e3\u6cd52. \u4f5c\u9876\u89d2\u4e3a36\u00b0\u3001\u8170\u957f\u4e3a1 \u7684\u7b49\u8170\u4e09\u89d2\u5f62ABC, BD\u4e3a\u5176\u5e95\u89d2B\u7684\u5e73\u5206\u7ebf\uff0c\u8bbeAD = x
\u5219AD = BD = BC = x, DC = 1 - x.
\u7531\u76f8\u4f3c\u4e09\u89d2\u5f62\u5f97\uff1ax2 = 1 - x
\u2234x = (\u221a 5 - 1)/2
\u2234sin18\u00b0 = x/2 = (\u221a5 - 1)/4.
由于54=18*3,36=18*2利用倍角公式
3x-4x^3=1-2x^2
4x^3-2x^2-3x+1=0
(x-1)(4x^2+2x-1)=0
4(x+1/4)^2=5/4
所以x=(√5-1)/4
cos18=根号(1-x^2)=√[2(5+√5)]/4
0.9510565
绛旓細cos18搴40鍒嗙瓑浜0.9474銆1搴︾瓑浜60鍒嗐備綑寮︼紙浣欏鸡鍑芥暟锛夛紝涓夎鍑芥暟鐨勪竴绉嶃備綑寮﹀畾鐞嗕害绉扮浜屼綑寮﹀畾鐞嗐傚叧浜庝笁瑙掑舰杈硅鍏崇郴鐨勯噸瑕佸畾鐞嗕箣涓銆傝瀹氱悊鏂█锛氫笁瑙掑舰浠讳竴杈圭殑骞虫柟绛変簬鍏朵粬涓よ竟骞虫柟鍜屽噺鍘昏繖涓よ竟涓庡畠浠す瑙掔殑浣欏鸡鐨勭Н鐨勪袱鍊嶃傛寮︼紝鏁板鏈锛屽湪鐩磋涓夎褰腑锛屼换鎰忎竴閿愯鈭燗鐨勫杈逛笌鏂滆竟鐨勬瘮鍙綔...
绛旓細sin36掳锛漜os54掳 鍗硈in锛2脳18掳锛夛紳cos锛3脳18掳锛2sin18掳cos18掳锛4(cos18掳)^3锛3cos18掳 鍥犱负cos18掳鈮0 鎵浠2sin18掳锛4(cos18掳)^2锛3 鏁寸悊寰4(sin18掳)锛2锛2sin18掳锛1锛0 瑙ｅ緱sin18掳=鈭(5-1 )/4鈮0.3090169 ...
绛旓細瑙ｏ細鈭祍in36掳锛漜os54掳 鍗硈in锛2脳18掳锛夛紳cos锛3脳18掳锛2sin18掳cos18掳锛4(cos18掳)^3锛3cos18掳 鈭礳os18掳鈮0 鈭2sin18掳锛4(cos18掳)^2锛3 鏁寸悊寰4(sin18掳)锛2锛2sin18掳锛1锛0 瑙ｅ緱sin18掳锛濓紙鏍瑰彿5锛1锛/4 ...
绛旓細鍒╃敤涓夎褰㈢浉浼硷紝鍙互鍒楀嚭(a+x)/a=a/x锛屽彲浠ュ皢a涓巟鐨勫叧绯昏В鍑烘潵锛屽厛寰楀嚭sin 18搴=x/2a锛屽啀鍒╃敤sin涓巆os鐨勫叧绯绘潵姹傚嚭cos 18搴銆
绛旓細cos(0.314) 鈮 1 - (0.314)^2/2 + (0.314)^3/24= 0.951107048 tan(0.314) 鈮 sin(0.314)/cos(0.314) = 0.308865579/0.951107048 鈮 0.324743234 鐩存帴璁＄畻 sin18掳= 0.309016994 cos18掳= 0.951056516 tan18掳= 0.324919696 璇樊 sin:(0.308865579 - 0.309016994)/0....
绛旓細cos7=0.992546151641322 cos8=0.9902680687415704 cos9=0.9876883405951378 cos10=0.984807753012208 cos11=0.981627183447664 cos12=0.9781476007338057 cos13=0.9743700647852352 cos14=0.9702957262759965 cos15=0.9659258262890683 cos16=0.9612616959383189 cos17=0.9563047559630355 cos18=0.9510565162951535 co...
绛旓細sin(18掳)绛変簬(鈭5-1)/4鈮0.309銆傚彲浠ョ湅鎴戜笅闈㈢殑璁＄畻鏂瑰紡锛氱敱sin36掳=cos54掳鍜屽嶈鍏紡锛屽緱2sin18掳cos18掳=4锛坈os18掳)^3-3cos18掳,cos18掳>0銆傛墍浠2sin18掳=4[1-锛坰in18掳)^2]-3銆傛墍浠4(sin18掳)^2+2sin18掳-1=0锛宻in18掳>0銆傛墍浠in18掳=锛堚垰5-1)/4銆傛寮︼紝鍦ㄧ洿瑙...
绛旓細瑙ｏ細鈭祍in36掳锛漜os54掳 鍗硈in锛2脳18掳锛夛紳cos锛3脳18掳锛2sin18掳cos18掳锛4(cos18掳)^3锛3cos18掳 鈭礳os18掳鈮0 鈭2sin18掳锛4(cos18掳)^2锛3 鏁寸悊寰4(sin18掳)锛2锛2sin18掳锛1锛0 瑙ｅ緱sin18掳锛濓紙鏍瑰彿5锛1锛/4 姝ｅ鸡鍑芥暟 涓鑸殑锛屽湪鐩磋鍧愭爣绯讳腑锛岀粰瀹氬崟浣嶅渾锛屽浠绘剰瑙...
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搴鐨勫肩害涓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
绛旓細璁＄畻锛歵an 18搴绛変簬澶氬皯锛堣鏈夊嚑鍒嗕箣鏍瑰彿鍑犵殑鍒嗘暟锛夛紵
