Find the radius of the circle circumscribed about the isosceles triangle whose sides are the solutions of the equation .
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$(MON 5)$ Find the radius of the circle circumscribed about the isosceles triangle whose sides are the solutions of the equation $x^2 - ax + b = 0$.
Izvor: Međunarodna matematička olimpijada, shortlist 1969
Školjka 
Find the radius of the circle circumscribed about the isosceles triangle whose sides are the solutions of the equation 
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