180-75=105
a/sin105=b/sin30
b=0,5a/sin105
S=0,25a^2sin45/sin105
sin105=sin(90+15)=cos15=(sqrt(3)+1)/(2*sqrt(2))
S=a^(2)/(2(sqrt(3)+1))=a^2*(sqrt(3)-1)/4
180-75=105
a/sin105=b/sin30
b=0,5a/sin105
S=0,25a^2sin45/sin105
sin105=sin(90+15)=cos15=(sqrt(3)+1)/(2*sqrt(2))
S=a^(2)/(2(sqrt(3)+1))=a^2*(sqrt(3)-1)/4