在四边形ABCD中,AC平分角BAD,角B=60度,AC=7,AD=6,三角形ACD的面积为15/2根3,求AB的长

S(△ACD)=AC*AD*sin∠CAD/2=15√3/2,sin∠CAD=5√3/14,cos∠CAD=√[1-(sin∠CAD)^2]=11/14,sin∠ACB=sin(180°-∠ABC-∠CAB)=sin(120°-∠CAB)=sin120°cos∠CAD-cos120°sin∠CAD=4√3/7.AB/sin∠ACB=AC/sin∠ABC,A...