Two Radicals on a Square

Problem

For x,y[0,1]x, y \in [0, 1], find the range of

f(x,y)=1+xy1+x2+1xy1+y2.f(x, y) = \sqrt{\frac{1 + xy}{1 + x^2}} + \sqrt{\frac{1 - xy}{1 + y^2}}.

Answer

Solution

Difficulty8/10
Topicsfunctions, algebra, Cauchy-Schwarz, inequality, Casework

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