Urgent! ! ! Ask someone to teach two questions in the first volume of the eighth grade math book! !

13.( 1) Because OE bisects AOB, EC is perpendicular to OA and ED is perpendicular to OB,

So ED=EC (the distance from a point on the bisector of the angle is equal to both sides of the angle),

So angle ECD= angle EDC.

(2) Because EC is perpendicular to OA and ED is perpendicular to OB.

EDC angle and CDO angle are complementary,

The angle ECD and the angle DCO are complementary,

Because angle ECD= angle EDC,

So, Angel ·CDO = Angel ·DCO,

So OC=OD.

③ Because OC=OD,

OE bisecting angle AOB,

So OE is perpendicular to DC and bisects DC.

1 1。 According to the equilateral triangle, it is proved that BAC and DAE are congruent.

So BC=DE.