应用正弦定理:a/sinA=b/sinB.
sinB=BsinA/a=5*sin120/12=5/24=5√3/24.
B=arcsin(5√3/24).
B≈21.15°,取整,B=21°.
C=180°-120°-21°=39°.
c/sinC=a/sinA.
c=asinC/SsinA.
=12*sin39/sin120=12*0.6293/0.866=8.65≈8.7 .
∴解得结果为:B=21°,C=39°,c=8.7cm.
应用正弦定理:a/sinA=b/sinB.
sinB=BsinA/a=5*sin120/12=5/24=5√3/24.
B=arcsin(5√3/24).
B≈21.15°,取整,B=21°.
C=180°-120°-21°=39°.
c/sinC=a/sinA.
c=asinC/SsinA.
=12*sin39/sin120=12*0.6293/0.866=8.65≈8.7 .
∴解得结果为:B=21°,C=39°,c=8.7cm.