如图所示在△ABC,AC=30,BC=70∠CAB=120°,线段AB=

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如图所示在△ABC,AC=30,BC=70∠CAB=120°,线段AB=
如图所示在△ABC,AC=30,BC=70∠CAB=120°,线段AB=

如图所示在△ABC,AC=30,BC=70∠CAB=120°,线段AB=

sinB/30=sin120°/70
sinB=3sin120°/7=3sin60°/7=3*√3/14≈0.3712,  ∠B=21.8°,∠C=180°-120°-21.8°=38.2°.
AB/sinC=70/sin120°,AB=70sinC/sin120°=70sin38.2°/sin60°=70*0.6184/0.866≈50.