Question 1128638
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If  {{{(x+y)^2}}} = 200,  then  x+y = +/-{{{sqrt(200)}}} = +/-{{{10*sqrt(2)}}}.


Then the average of x and y is  {{{(x+y)/2}}} = plus OR minus  {{{5*sqrt(2)}}}.    <U>ANSWER</U>
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The rest of the condition is IRRELEVANT and does not influence or change the answer.