12 trigonometri

m(EBC)=b olsun
m(DBA)=c olsun
a+b+c=90
a=90-(b+c)
tana=tan(90-(b+c))=cot(b+c)
cotb=13/7 cotc=1
cot(b+c)=(cotb.cotc-1)/(cotb+cotc)=(13/7 -1)/(13/7 +1)=
6/7/20/7=6/20=3/10
CEVAP B