Angle ABD = Angle BDE (Alternate Angles) Since the sides |BD| and |BE| are equal (Base angles of isosceles triangle are the same), Angle BDE= Angle BED Angles on a straight line sum up to 180∘ ABD+2x+56=180 ABD=180−56−2x ABD=124−2x But ABD=BDE and BDE=BED ABD=BDE=BED=124−2x But angles in a triangle sum up to 180∘ 2x+124−2x+124−2x=180 2x−2x−2x+124+124=180 −2x+248=180 248−180=2x 68=2x Divide both sides by 2 68∕2=2x∕2 34=x x=34