有没有会的大神，求具体解答过程！
consider △ADC
AD/sin60° = CD/sin(180°-60°-54°)
AD/sin60° = CD/sin66° (1)
consider △ABD
AB/sin(180°-54°) = AD/sin∠B
AB/sin126° = AD/sin∠B
AB/sin54° = AD/sin∠B (2)
cosider △ABC
AC/sin∠B = AB/sin60° (3)
AB=AC+CD (4)
from (3) and (4)
AB=AC+CD
AB= AB(sin∠B/sin60°)+CD (5)
from (2) and (5)
AB= AB(sin∠B/sin60°)+CD
AD(sin54°/sin∠B)= AD(sin54°/sin∠B)(sin∠B/sin60°)+CD
AD(sin54°/sin∠B)= AD(sin54°/sin60°)+CD (6)
from (1) and (6)
AD(sin54°/sin∠B)= AD(sin54°/sin60°)+CD
CD(sin60°/sin66°)(sin54°/sin∠B)= CD(sin60°/sin66°)(sin54°/sin60°)+CD
(sin60°.sin54°)/(sin66°.sin∠B)= (sin54°/sin66°)+1
sin∠B =(sin60°.sin54°).[(sin54°/sin66°)+1]/sin66°
