Given that AB=AC⇒ Angle C= Angle B (1) AD and BE are altitudes ⇒ they make 90 degrees with the sides Angle AOB=105⇒ Angle EOD =105 (Vertically Opposite Angles) In quadrilateral DOEC Angle C=360−105−90−90=75⇒ Angle B=75 (from 1) We know that from the area of the triangle AD*BC=BE*AC