Convex Functions: Proving g(x) is Convex

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To prove that g(x) = (f(x))^2 is convex given that f(x) is convex and positive on a convex set S, one can use the definition of convexity. A function is convex if its second derivative is non-negative. Since f(x) is convex, its first derivative f'(x) is non-decreasing, and the second derivative f''(x) is non-negative. By applying the chain rule and properties of derivatives, it can be shown that g''(x) = 2f'(x)f'(x) + 2f(x)f''(x) is non-negative, confirming that g(x) is convex. Thus, if f(x) is convex, then g(x) is also convex.
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let f(X) : Rn --> R be a function defined on convex set S s.t S is a subset of
Rn (real space n-dim). Let f is positive throughout. Then define g(x) = (f(x))^2. Prove that if f(x) is convex then g(x) is also convex.
 
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russel.arnold said:
let f(X) : Rn --> R be a function defined on convex set S s.t S is a subset of
Rn (real space n-dim). Let f is positive throughout. Then define g(x) = (f(x))^2. Prove that if f(x) is convex then g(x) is also convex.

This needs to be posted in the Calculus and Beyond Homework forum with your attempt at a solution.
 
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