admin百科知識 2022-02-13 9:21:42 設△ABC的內角A、B、C所對應的邊分別爲a、b、c,cos(A-C)+cosB=32,b2=ac,則B=_.設△ABC的內角A、B、C所對應的邊分別爲a、b、c,cos(A-C) cosB=32,b2=ac,則B=______.網友廻答:匿名網友∵B=π-(A C),∴已知等式變形得:cos(A-C)-cos(A C)=32,即cosAcosC sinAsinC-cosAcosC sinAsinC=2sinAsinC=32,∴sinAsinC=34,將b2=ac利用正弦定理化簡得:sin2B=sinAsinC=34,∴sinB=32或sinB=-32(捨去)... db標簽 生活常識_百科知識_各類知識大全»設△ABC的內角A、B、C所對應的邊分別爲a、b、c,cos(A-C)+cosB=32,b2=ac,則B=_.
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