cos18度44'25''的值
cos18\u7684\u503c\u8bbesin18=x,\u5219sin54=sin(90-36)=cos36
\u7531\u4e8e54=18*3,36=18*2\u5229\u7528\u500d\u89d2\u516c\u5f0f
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
\u6240\u4ee5x=(\u221a5-1)/4
cos18=\u6839\u53f7(1-x^2)=\u221a[2(5+\u221a5)]/4
\u5e94\u8be5\u662fsinx=¼(\u221a5\uff0d1)
\u4f60\u53ef\u4ee5\u770b\u770b\u53c2\u8003\u8d44\u6599\u91cc\u7684
sin18>0
\u6240\u4ee5-0.9\u820d\u53bb
\u4e0d\u77e5\u4f601/2\u600e\u4e48\u5f97\u5230
\u4f46\u5c31\u7b97=1/2
\u5219\u662fsin30=1/2
\u4e0d\u662fsin18
≈cos18.7403゜
≈0.947
绛旓細cos18銈44'25''鈮坈os18.7403銈 鈮0.947
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cos18=鏍瑰彿(1-x^2)=鈭歔2(5+鈭5)]/4
绛旓細0.951056516295銆傛牴鎹煡璇綔涓氬府寰楃煡锛宑os鏈川鏄换鎰忚鐨勯泦鍚堜笌涓涓瘮鍊肩殑闆嗗悎鐨勫彉閲忎箣闂寸殑鏄犲皠锛屾墍浠cos18搴绛変簬0.951056516295銆
绛旓細璁緎in18=x,鍒檚in54=sin(90-36)=cos36 鐢变簬54=18*3,36=18*2鍒╃敤鍊嶈鍏紡 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 鎵浠=(鈭5-1)/4 cos18=鏍瑰彿(1-x^2)=鈭歔2(5+鈭5)]/4 ...
绛旓細鐢ㄨ绠楀櫒绠楋細0.95105651629515357211643933337938 鎵嬬畻锛氭彁绀 鍏抽敭18*3=90-2*18 鍜cos3x=cos锛坸+2x锛=4锛坈osx锛塣3-3cosx 鍙傝冭祫鏂欙細鑻忔暀鐗堟暟瀛︿功锛屽繀淇4锛孭116
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0.95105652
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(1)=(2)(绾﹀幓cos18掳鈮0)2sin18掳=cos36掳-2sin18掳骞虫柟 2sin18掳=1-2sin18掳骞虫柟-2sin18掳骞虫柟 2sin18掳=1-4sin18掳骞虫柟 4sin18掳骞虫柟+2sin18掳-1=0,浠=sin18掳鈫 4x骞虫柟+2x-1=0,鐢辨眰鏍瑰叕寮 x=(-2卤2鈭5)/8=(-1卤鈭5)/4,璐熸牴涓嶅悎 x=(-1+鈭5)/4=(鈭5-1)...
