在三角行内sin18度等于多少啊 ??? sin18度等于多少?
sin18\u5ea6\u7b49\u4e8e\u591a\u5c11\u600e\u4e48\u8ba1\u7b97\uff1f\u8c22\u8c22\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.
\u89e3\uff1a\u2235sin36\u00b0\uff1dcos54\u00b0
\u5373sin\uff082\u00d718\u00b0\uff09\uff1dcos\uff083\u00d718\u00b0\uff09
2sin18\u00b0cos18\u00b0\uff1d4(cos18\u00b0)^3\uff0d3cos18\u00b0
\u2235cos18\u00b0\u22600
\u22342sin18\u00b0\uff1d4(cos18\u00b0)^2\uff0d3
\u6574\u7406\u5f974(sin18\u00b0)\uff3e2\uff0b2sin18\u00b0\uff0d1\uff1d0
\u89e3\u5f97sin18\u00b0\uff1d\uff08\u6839\u53f75\uff0d1\uff09/4
\u6b63\u5f26\u51fd\u6570
\u4e00\u822c\u7684\uff0c\u5728\u76f4\u89d2\u5750\u6807\u7cfb\u4e2d\uff0c\u7ed9\u5b9a\u5355\u4f4d\u5706\uff0c\u5bf9\u4efb\u610f\u89d2\u03b1\uff0c\u4f7f\u89d2\u03b1\u7684\u9876\u70b9\u4e0e\u539f\u70b9\u91cd\u5408\uff0c\u59cb\u8fb9\u4e0ex\u8f74\u975e\u8d1f\u534a\u8f74\u91cd\u5408\uff0c\u7ec8\u8fb9\u4e0e\u5355\u4f4d\u5706\u4ea4\u4e8e\u70b9P\uff08u\uff0cv\uff09\uff0c\u90a3\u4e48\u70b9P\u7684\u7eb5\u5750\u6807v\u53eb\u505a\u89d2\u03b1\u7684\u6b63\u5f26\u51fd\u6570\uff0c\u8bb0\u4f5cv=sin\u03b1\u3002\u901a\u5e38\uff0c\u6211\u4eec\u7528x\u8868\u793a\u81ea\u53d8\u91cf\uff0c\u5373x\u8868\u793a\u89d2\u7684\u5927\u5c0f\uff0c\u7528y\u8868\u793a\u51fd\u6570\u503c\uff0c\u8fd9\u6837\u6211\u4eec\u5c31\u5b9a\u4e49\u4e86\u4efb\u610f\u89d2\u7684\u4e09\u89d2\u51fd\u6570y=sin x\uff0c\u5b83\u7684\u5b9a\u4e49\u57df\u4e3a\u5168\u4f53\u5b9e\u6570\uff0c\u503c\u57df\u4e3a[-1,1]\u3002
即sin(2×18°)=cos(3×18°)
2sin18°cos18°=4(cos18°)^3-3cos18°
∵cos18°≠0
∴2sin18°=4(cos18°)^2-3
整理得4(sin18°)^2+2sin18°-1=0
解得sin18°=(根号5-1)/4
sin18度=(根号5-1)/4
cos18度=(根号(10+2根号5))/4
tan18度=根号((5-2根号5)/5)
cot18度=根号(5+2根号5)
sec18度=根号((10-2根号5)/5)
csc18度=根号5+1
sin18度=(根号5-1)/4
cos18度=(根号(10+2根号5))/4
tan18度=根号((5-2根号5)/5)
cot18度=根号(5+2根号5)
sec18度=根号((10-2根号5)/5)
csc18度=根号5+1
解:∵sin36°=cos54°
即sin(2×18°)=cos(3×18°)
2sin18°cos18°=4(cos18°)^3-3cos18°
∵cos18°≠0
∴2sin18°=4(cos18°)^2-3
整理得4(sin18°)^2+2sin18°-1=0
解得sin18°=(根号5-1)/4
sin18=(根号5-1)/4
绛旓細sin18=0.309016994 cos36=0.809016994
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绛旓細瑙e緱a1=(1+鈭5)b/2锛宎2=(1涓鈭5)b/2(涓嶅悎棰樻剰鑸嶅幓)銆侫B=(鈭5+1)BC/2銆傚欢闀緽A鑷矱锛屼娇AE=AC锛岃繛鎺C 鍒<AEC=<ACE=18搴锛<ECB=<ECA+<ABC=72搴+18搴=90搴 杩嘇鐐逛綔AF//BC锛屼氦EC浜嶧蹇呭钩鍒咵C锛孉F=BC/2=b/2 鍒涓夎褰EAF涓Rt涓夎褰紝<EFA=<ECB=90搴 鍦≧t涓夎褰FA涓:s鈪...
绛旓細/BC 瑙e緱BC=锛堚垰5-1锛/2*AC 鍋欰H鈯C浜嶩锛屽垯鈭燞AC=18锛孒C=BC/2=锛堚垰5-1锛/4*AC sin18=sinHAC=HC/AC=锛堚垰5-1锛/4 琛ュ厖锛5X²-15X-AX+3A=0 锛坸-3锛夛紙5x-A锛=0 涓ゆ牴涓簒1=3锛寈2=A/5 鍥犱负sinA<1 sinA=A/5 sinB/B=sinA/A=1/5锛宻inB=1锛岃B涓虹洿瑙掞紝A=4 ...
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绛旓細绛変簬-0.555992銆傛寮︼紙sine锛夛紝鏁板鏈锛屽湪鐩磋涓夎褰腑锛屼换鎰忎竴閿愯A鐨勫杈逛笌鏂滆竟鐨勬瘮鍙仛瑙扐鐨勬寮︼紝璁颁綔sinA锛堢敱鑻辫sine涓璇嶇畝鍐欏緱鏉ワ級锛屽嵆sinA=瑙扐鐨勫杈规瘮鏂滆竟銆