在三角形ABC中,若A=2B则a等于
A=2B正弦定理：a/sinA=b/sinB
sinA=sin2B=2sinBcosB
a=b/sinB*sinA=2bcosB
绛旓細c^2=a^2+b^2-2ab*cosC 灏A=2B鍗矪=A/2甯﹀叆,寰 C^2=锛5/4-cosC锛塧^2 (a/c)^2=1/(5/4-cosC) 閿愯涓夎褰腑,0
绛旓細瑙ｏ細鍦ㄥ湪RT涓夎褰BC涓 a²+b²=c²鍥犱负a=2b锛c=4 鎵浠ワ紙2b锛²+b²=4²5b²=16 b²=16/5 b=鈭氾紙16/5锛塨=锛4鈭5锛/5 a=2b=2*锛4鈭5锛/5=(8鈭5锛/5
绛旓細瑙ｏ細寤堕暱BA浣緼D=AC,杩炴帴CD,杩嘋鍋欳E鈯B浜嶦,鈭碅C=AD=4,鈭燚=鈭燚CA=1/2*鈭燙AB=鈭燘,鍒欌柍ABC涓虹瓑鑵涓夎褰銆傗埖CE鈯B锛屸埓DE=BE=1/2*BD=1/2*(AD+AB)=1/2*(4+5)=9/2 AE=AB-BE=5-9/2=1/2 鍙圕E^2=AC^2-AE^2=16-1/4 鈭碆C^2=CE^2+BE^2=16-1/4+81/4=36 鈭碆C=...
绛旓細A=2B锛鎵浠 sinA=sin2B , sinA = 2 sinB cosB , 鎵浠osB = sinA /2sinB 鐢辨寮﹀畾鐞嗗緱 cosB = sinA /2sinB =a/2b= 鈭5/4
绛旓細(2b²-a²-b²+c²)/2b=鈭3/3c脳sinA (b²+c²-a²)/2b=鈭3/3c脳sinA (b²+c²-a²)/2bc=鈭3/3脳sinA cosA=鈭3/3脳sinA sinA/cosA=3/鈭3=鈭3 tanA=鈭3 鈭礎鏄涓夎褰BC鍐呰 鈭A=60掳 2銆乤²=b²+c&...
绛旓細姝ら涓烘寮﹀畾鐞嗙殑缁煎悎搴旂敤锛岃鐐规槸瑙掑寲杈规垨杈瑰寲瑙 鍏蜂綋璇佹槑杩囩▼濡備笅锛1.鍏呭垎鎬 鍥犱负 A=2B 鎵浠 sinC=sin(A+B)=sin3B 鎵浠(sinB+sinC)/sinA=[1-(sinB)^2+3(cosB)^2)]/2cosB=2cosB 姝ゅ鐢ㄥ埌浜嗘寮︿笁鍊嶈鍏紡锛歴in3B=-(sinB)^3+3sinB(cosB)^2 鍥犱负 sinA/sinB=2sinBcosB/sinB=2...
绛旓細b²=a²+c²-2ac•cosB 鈭碼²+2b²-3ab=0锛屸憼 鈭礢=1/2•acsinB=鈭3/2锛屸埓ab=2锛屸憽 鑱旂珛鈶犫憽寰锛宎=2锛宐=1锛庛愯冪偣銆戯細涓夎褰姝ｅ鸡瀹氱悊涓庝綑寮﹀畾鐞嗙殑缁煎悎搴旂敤锛//--- 銆愭槑鏁欍戜负鎮ㄨВ绛旓紝濡傝嫢婊℃剰,璇风偣鍑汇愰噰绾充负婊℃剰鍥炵瓟銆;濡傝嫢鎮ㄦ湁涓嶆弧鎰忎箣...
绛旓細a=2bcosC 鐢辨寮﹀畾鐞嗗緱sinA=2sinBcosC sin(B+C)=2sinBcosC sinBcosC+cosBsinC=2sinBcosC sinBcosC-cosBsinC=0 sin(B-C)=0 B銆丆涓轰笁瑙掑舰鍐呰 0<B<蟺 0<C<蟺 -蟺<B-C<蟺锛屽湪鍖洪棿(-蟺锛屜)涓婂彧鏈塻in0=0 B-C=0 B=C b=c 涓夎褰㈡槸绛夎叞涓夎褰傚綋鐒朵笁瑙掑舰鍙兘鏄瓑鑵扮洿瑙涓夎褰...
绛旓細鐢辨寮﹀畾鐞嗭細a/sinA=b/sinB锛屽彲寰楋細sinB=(bsinA)/a锛岃嫢 a=2bsinA锛屽垯 (bsinA)/a=1/2锛屾墍浠 sinB=1/2,鍥犱负 B鏄涓夎褰鐨勫唴瑙掞紝鎵浠 B=30搴 鎴 B=150搴︺
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