已知:在△ABC中.AB、AC的垂直平分线分别交BC于点E.F.
(1)如图1.∠B=∠C=30°.求∠EAF的度数.
(2)如图2.AB≠AC.且90°<∠BAC<180°
①若∠BAC=140°.则∠EAF=___°:若∠BAC=n°.则∠EAF=___
②当∠BAC=___°时.AE⊥AF.
③若BC=a.则△AEF的周长为___.