Question 1153570
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            This problem is for advanced students  (Math circle level or  Math  Olympiad level).


            Therefore,  I will be very short and will give the basic idea,  only.



<pre>
The given data allow to determine the side length of the given square.



    How to do it, you will find in the lesson
  
        - <A HREF=https://www.algebra.com/algebra/homework/word/geometry/Find-the-side-of-a-square-if-distances-are-given-from-an-interior-point-to-3-its-vertices.lesson>Find the side of a square if distances are given from an interior point to 3 its vertices</A> 

    in this site, where similar problem was solved.



By knowing the square side length, you may apply then the Cosine Law and to find the angle ETF.
</pre>

Happy learning and happy solving (!)