In a square ABCD,its diagonal AC and BD intersect eachother at point O.The bisector of angle DAO meets BD at point M and the bisector of angle ABD meets AC at N and AM at L.show that:

(a)angle ONL+angle OML=180 degree.

(b)angle BAM=angle BMA

(c)ALOB is a cyclic quadrilateral.

Hi!
Here is the answer to your question.
 
ABCD is a square.
(c) In quadrilateral OMNL, ∠ONL + ∠OML + ∠NOM + ∠NLM = 360°
⇒ 180° + 90° + ∠NLM = 360° [∠ONL + ∠OML = 180°]
⇒ ∠NLM = 90°
∠NLM + ∠ALB = 180°
⇒ 90° + ∠ALB = 180°
⇒ ∠ALB = 90°
∠ALB = ∠AOB   (Each 90°)
It is known that If a line segment joining two points subtends equal angles at two other points lying on the same side of the line containing the line segment, the four points lie on a circle (i.e. they are concyclic).
Thus, ALOB is a cyclic quadrilateral.
 
 
Cheers!

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