Question 1209119
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x^2 + y^2 = x^2 -2xy + y^2 + 2xy = (x^2 -2xy + y^2) + 2xy = (x-y)^2 + 2xy = 99^2 + 2*630 = 11061.    <U>ANSWER</U>
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Solved.


The idea of the solution is to present the sum of the squares (the desired value) 
via given information by a simplest way, using well known identities.


It is how this problem is designed and how to it is expected to be solved.