(2) Answer: The quantitative relationship among OA, AD and AC is OA+AC=AD, which proves that OA+AC=AD because OB=AB, BC=BD, angle OBC= angle OBA+ angle ABC=60 degrees+angle DBC+ angle ABC= angle ABD, and triangle OBC is congruent triangles ABD.

(3) The position of point E has not changed. Let the straight line AD be Y=kX+b, and A(a, 0) and D(m, n) are known as

0=ka+b，n=km+b，k=n/(m-a)，b=an/(a-m)，

So the square of AE= (an)/ (a-m)+the square of A = the square of N+the square of (a-m).