We have to simplify the expression , it means
we have to try to factor every number and and every variable , and try to factor out those which can be factored out from the square root
first number is 625
Lets try to write prime factors of 625
625 = 5*5*5*5
Next are x^20 and y^8
Now square root will divide each exponent by 2
So we get

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So this is the answer.