Chapter 5: Problem 14
Let \(x \in \mathbb{R}, x>0\). Show that if \(m, p \in \mathbb{Z}, n, q \in \mathbb{N}\), and \(m q=n p\), then \(\left(x^{1 / n}\right)^{m}=\left(x^{1 / q}\right)^{p}\).
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Chapter 5: Problem 14
Let \(x \in \mathbb{R}, x>0\). Show that if \(m, p \in \mathbb{Z}, n, q \in \mathbb{N}\), and \(m q=n p\), then \(\left(x^{1 / n}\right)^{m}=\left(x^{1 / q}\right)^{p}\).
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Let \(h: \mathbb{R} \rightarrow \mathbb{R}\) be continuous on \(\mathbb{R}\) satisfying \(h\left(m / 2^{n}\right)=0\) for all \(m \in \mathbb{Z}, n \in \mathbb{N} .\) Show that \(h(x)=0\) for all \(x \in \mathbb{R}\)
Let \(I:=[0,1]\) and let \(f: I \rightarrow \mathbb{R}\) be defined by \(f(x):=x\) for \(x\) rational, and \(f(x):=1-x\) for \(x\) irrational. Show that \(f\) is injective on \(I\) and that \(f(f(x))=x\) for all \(x \in I\). (Hence \(f\) is its own inverse function!) Show that \(f\) is continuous only at the point \(x=\frac{1}{2}\).
Give an example of functions \(f\) and \(g\) that are both discontinuous at a point \(c\) in \(\mathbb{R}\) such that (a) the sum \(f+g\) is continuous at \(c\), (b) the product \(f g\) is continuous at \(c\).
Suppose that \(f\) is a continuous additive function on \(\mathbb{R}\). If \(c:=f(1)\), show that we have \(f(x)=c x\) for all \(x \in \mathbb{R}\). [Hint: First show that if \(r\) is a rational number, then \(f(r)=c r\). ]
Show that both \(f(x):=x\) and \(g(x):=x-1\) are strictly increasing on \(I:=[0,1]\), but that their product \(f g\) is not increasing on \(I\).
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