Problem

Problem

If f(x)=1−x1+x,x>0f(x) = \frac{1-x}{1+x}, x > 0 , and y=f(f(x))+f(f(1x))y = f(f(x)) + f\left(f\left(\frac{1}{x}\right)\right) , the least value of yy is given by (a) 1 (b) 2 (c) 3 (d) 4
Intuitive explanation

The key is recognizing that function composition often simplifies dramatically—especially when the function has a special structure. Calculate f(f(x))f(f(x)) and f(f(1/x))f(f(1/x)) explicitly, then look for how they combine. You'll likely find that yy reduces to a much simpler expression in xx, and then finding its minimum becomes a straightforward calculus or inequality problem. The symmetry in the problem setup suggests the answer might be elegant.

Intuitive explanation

The key is recognizing that function composition often simplifies dramatically—especially when the function has a special structure. Calculate f(f(x))f(f(x)) and f(f(1/x))f(f(1/x)) explicitly, then look for how they combine. You'll likely find that yy reduces to a much simpler expression in xx, and then finding its minimum becomes a straightforward calculus or inequality problem. The symmetry in the problem setup suggests the answer might be elegant.

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