2013-10-20
展开全部
a�0�5-c�0�5=2b,且sinAcosC=3cosAsinC,
sinAcosC-3cosAsinC=0,
sinAcosC+cosAsinC-4cosAsinC=0
sin(A+C)-4cosAsinC=0
sinB=4cosAsinC
b=4ccosA,(1/2)b�0�5=2bccosA
b�0�5+c�0�5-a�0�5=2bccosA=(1/2)b�0�5
b�0�5-2b=(1/2)b�0�5,解得b=4
sinAcosC-3cosAsinC=0,
sinAcosC+cosAsinC-4cosAsinC=0
sin(A+C)-4cosAsinC=0
sinB=4cosAsinC
b=4ccosA,(1/2)b�0�5=2bccosA
b�0�5+c�0�5-a�0�5=2bccosA=(1/2)b�0�5
b�0�5-2b=(1/2)b�0�5,解得b=4
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