Angle Bisector

Three statements are given below: I. In a ||gm, the angle bisectors of two adjacent angles enclose a right angle. I. The angle bisectors of a ||gm form a rectangle. III. The triangle formed by joining the midpoints of the sides of an isosceles triangle is not necessarily an isosceles triangle. Which is true?

Prove that the angle between internal bisector of one base angle and the external bisector of the other base angle of a triangle is equal to one-half of the vertical angle.

Prove that the angle between internal bisector of one base angle and the external bisector of the other base angle of a triangle is equal to one half of the vertical angle.