Consider the +X axis and the +Y axis to be the corner. The table has radius r which puts the center of the circle at (r,r) and makes the circle tangent to both axis. The equation of the circle (table's perimeter) is

(x-r)^2 + (y-r)^2 = r^2 .

This leads to

r^2 - 2r(x+y) + x^2 + y^2 = 0

Using x = 10, y = 5 we get the solutions 25 and 5. The former is the radius of the table. Its diameter is 50 cm.

The latter number is the radius of a table that has a point which satisfies the conditions but is not on the quarter circle nearest the corner.

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