Let f be a differentiable real function defined in (a, b). Prove that f is convex if and only if f' is monotonically increasing. Assume next that f"(x) exists for every x e (a, b), and prove that f is convex if and only if f"(x)20 for all x e (a, b).
Let f be a differentiable real function defined in (a, b). Prove that f is convex if and only if f' is monotonically increasing. Assume next that f"(x) exists for every x e (a, b), and prove that f is convex if and only if f"(x)20 for all x e (a, b).
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Step 1
A function f is convex in a domain if for all , .
Also if a function is monotonically incresing then implies that .
The derivative of a function exists then it can be expressed using the limit definitions.
Now a differentiable function is convex if it graph lies above all of its tangents.
Also, it is known that if , then .
The theorem can be proved using all these results.
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