Hi,
Since DOC is equilateral triangle, DC = DO also since all sides of square are equal DC = AD. Thus, AOD is equilateral. Using, sum of angles of triangle = 180 we find the value of DAO

Thank you Sir, it was easy problem, just could not see it through.

Height of an equilateral triangle is √3/2. Hence the triangle will lie within the square.

Hi Aquir,

Since DOC is an equilateral triangle, DO=DC.

ABCD is a square => AD= DC

=> DO = AD

Therefore AOD is an isosceles triangle.