# Kurs:Mathematik für Anwender (Osnabrück 2011-2012)/Teil I/Arbeitsblatt 16/en

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Warm-up-exercises

### Exercise

Find a zero for the function

$f\colon \mathbb {R} \longrightarrow \mathbb {R} ,\,x\longmapsto f(x)=x^{2}+x-1,$ in the interval ${}[0,1]$ using the interval bisection method with a maximum error of ${}1/100$ .

### Exercise

Let

$f\colon [0,1]\longrightarrow [0,1[$ be a continuous function. Prove that ${}f$ is not surjective.

### Exercise

Give an example of a bounded interval ${}I\subseteq \mathbb {R}$ and a continuous function

$f\colon I\longrightarrow \mathbb {R}$ such that the image of ${}f$ is bounded, but the function admits no maximum.

### Exercise

Let

$f\colon [a,b]\longrightarrow \mathbb {R}$ be a continuous function. Show that there exists a continuous extension

${\tilde {f}}\colon \mathbb {R} \longrightarrow \mathbb {R}$ of ${}f$ .

### Exercise

Let

$f\colon I\longrightarrow \mathbb {R}$ be a continuous function defined over a real interval. The function has at points ${}x_{1},x_{2}\in I$ , ${}x_{1} , local maxima. Prove that the function has between ${}x_{1}$ and ${}x_{2}$ has at least one local minimum.

### Exercise

Determine directly, for which ${}n\in \mathbb {N}$ the power function

$\mathbb {R} \longrightarrow \mathbb {R} ,\,x\longmapsto x^{n},$ has an extremum at the point zero.

### Exercise

Show that the Intermediate value theorem for continuous functions from ${}\mathbb {Q}$ to ${}\mathbb {Q}$ does not hold.

### Exercise

Determine the limit of the sequence

$x_{n}={\sqrt {\frac {7n^{2}-4}{3n^{2}-5n+2}}},\,n\in \mathbb {N} .$ Hand-in-exercises

### Exercise (2 points)

Determine the minimum of the function

$f\colon \mathbb {R} \longrightarrow \mathbb {R} ,\,x\longmapsto x^{2}+3x-5.$ ### Exercise (4 points)

Find for the function

$f\colon \mathbb {R} \longrightarrow \mathbb {R} ,\,x\longmapsto f(x)=x^{3}-3x+1,$ a zero in the interval ${}[0,1]$ using the interval bisection method, with a maximum error of ${}1/200$ .

### Exercise (2 points)

Determine the limit of the sequence

$x_{n}={\sqrt[{3}]{\frac {27n^{3}+13n^{2}+n}{8n^{3}-7n+10}}},\,n\in \mathbb {N} .$ The next task uses the notion of an even and an odd function.

A function

$f\colon \mathbb {R} \longrightarrow \mathbb {R}$ is called even, if for all ${}x\in \mathbb {R}$ the equality
$f(x)=f(-x)$ holds. A function
$f\colon \mathbb {R} \longrightarrow \mathbb {R}$ is called odd, if for all ${}x\in \mathbb {R}$ the equality
$f(x)=-f(-x)$ holds.

### Exercise (4 points)

Let

$f\colon \mathbb {R} \longrightarrow \mathbb {R}$ be a continuous function. Show that one can write

$f=g+h$ with a continuous even function ${}g$ and a continuous odd function ${}h$ .

The following task uses the notion of fixed point.

Let ${}M$ be a set and let

$f\colon M\longrightarrow M$ be a function. An element ${}x\in M$ such that ${}f(x)=x$ is called a fixed point of the function.

### Exercise (4 points)

Let

$f\colon [a,b]\longrightarrow [a,b]$ be a continuous function from the interval ${}[a,b]$ into itself. Prove that ${}f$ has a fixed point.