If we use the corners of the square as circle centres, with radius "x",
and using the fact that the angle at the centre of a circle is twice the angle at the circumference
for angles standing on a common arc,
then it follows that if angle ACE is 30, then the angles ADE and AED are 15 degrees.
Triangle AGC is equilateral as all sides are R.
The angles of AGC are all , so