Chapter 5: Problem 15
Examine which open [respectively, closed] intervals are mapped by \(f(x):=x^{2}\) for \(x \in \mathbb{R}\) onto open [respectively, closed] intervals.
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Chapter 5: Problem 15
Examine which open [respectively, closed] intervals are mapped by \(f(x):=x^{2}\) for \(x \in \mathbb{R}\) onto open [respectively, closed] intervals.
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Give an example of a function \(f:[0,1] \rightarrow \mathbb{R}\) that is discontinuous at every point of \([0,1]\) but such that \(|f|\) is continuous on \([0,1]\).
If \(f_{0}(x):=1\) for \(x \in[0,1]\), calculate the first few Bernstein polynomials for \(f_{0}\). Show that they coincide with \(f_{0}\). [Hint: The Binomial Theorem asserts that $$ \left.(a+b)^{n}=\sum_{k=0}^{n}\left(\begin{array}{l} n \\ k \end{array}\right) a^{k} b^{n-k} .\right] $$
Let \(I:=[0, \pi / 2]\) and let \(f: I \rightarrow \mathbb{R}\) be defined by \(f(x):=\sup \left\\{x^{2}, \cos x\right\\}\) for \(x \in I .\) Show there exists an absolute minimum point \(x_{0} \in I\) for \(f\) on \(I .\) Show that \(x_{0}\) is a solution to the equation \(\cos x=x^{2}\)
If \(g(x):=\sqrt{x}\) for \(x \in[0,1]\), show that there does not exist a constant \(K\) such that \(|g(x)| \leq K|x|\) for all \(x \in[0,1]\). Conclude that the uniformiy continuous \(g\) is not a Lipschitz function on \([0,1]\).
Let \(f(x):=x\) for \(x \in[0,1]\), and \(f(x):=1+x\) for \(x \in(1,2]\). Show that \(f\) and \(f^{-1}\) are strictly increasing. Are \(f\) and \(f^{-1}\) continuous at every point?
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