\[ \begin{array}{l}
f(x)=x\textrm{ arctg } x\\
1. \ \ D=\mathbb{R}\\
2. \ \ f(-x)=-x\cdot \textrm{ arctg}(-x)=-x \cdot (-\textrm{ arctg} x)=x\textrm{ arctg} x=f(x) - \textrm{ funkcja parzysta }
\\
3. \ \ x=0 \ \ \Rightarrow \ \ f(0)=0\cdot \textrm{ arctg } 0=0\\
f(x)=0 \ \ \Rightarrow \ \ x\textrm{ arctg } x=0 \ \ \Rightarrow \ \ x=0 \ \ \vee \ \ \textrm{ arctg } x=0 \ \ \Leftrightarrow \ \ x=0\\
(0,0) - \textrm{ punkt przecięcia z osiami układu współrzędnych}\\
\\
{\displaystyle 4. \ \ \lim_{x \to \infty}x\textrm{ arctg } x=\left [ \infty \cdot \frac{\pi}{2} \right ]=\infty}
\\
{\displaystyle \lim_{x \to -\infty}x\textrm{ arctg } x=\left [ -\infty \cdot \left (-\frac{\pi}{2} \right ) \right ]=\infty}
\\
{\displaystyle A= \lim_{x \to \infty}\frac{f(x)}{x}=\lim_{x \to \infty} \textrm{ arctg } x=\frac{\pi}{2}}\\
{\displaystyle B=\lim_{x \to \infty}\left [ f(x)- \frac{\pi}{2} x\right ]=\lim_{x \to \infty}\left [ x\textrm{ arctg } x - \frac{\pi}{2} x\right ]=\lim_{x \to \infty}\left [ x\left (\textrm{ arctg } x - \frac{\pi}{2} \right )\right ]=\left [ \infty \cdot 0 \right ]= \lim_{x \to \infty} \frac{\textrm{ arctg } x - \frac{\pi}{2} }{\frac{1}{x}}=\left [ \frac{0}{0} \right ] \stackrel{H}=}\\
{\displaystyle =\lim_{x \to \infty} \frac{ \frac{1}{1+x^{2}} }{-\frac{1}{x^{2}}}=\lim_{x \to \infty}\frac{-x^{2}}{1+x^{2}}=\lim_{x \to \infty}\frac{-1}{\frac{1}{x^{2}}+1}=\lim_{x \to \infty}\frac{-1}{\cancelto{0}{\frac{1}{x^{2}}}+1}=-1}\\
{\displaystyle y=\frac{\pi}{2}x-1 - \textrm{asymptota ukośna prawostronna}}\\
\\
{\displaystyle A= \lim_{x \to -\infty}\frac{f(x)}{x}=\lim_{x \to -\infty} \textrm{ arctg } x=-\frac{\pi}{2}}\\
{\displaystyle B=\lim_{x \to -\infty}\left [ f(x)+ \frac{\pi}{2} x\right ]=\lim_{x \to -\infty}\left [ x\textrm{ arctg } x + \frac{\pi}{2} x\right ]=\lim_{x \to -\infty}\left [ x\left (\textrm{ arctg } x + \frac{\pi}{2} \right )\right ]=\left [ -\infty \cdot 0 \right ]= \lim_{x \to -\infty} \frac{\textrm{ arctg } x + \frac{\pi}{2} }{\frac{1}{x}}=\left [ \frac{0}{0} \right ] \stackrel{H}=}\\
{\displaystyle =\lim_{x \to -\infty} \frac{ \frac{1}{1+x^{2}} }{-\frac{1}{x^{2}}}=\lim_{x \to -\infty}\frac{-x^{2}}{1+x^{2}}=\lim_{x \to -\infty}\frac{-1}{\frac{1}{x^{2}}+1}=\lim_{x \to -\infty}\frac{-1}{\cancelto{0}{\frac{1}{x^{2}}}+1}=-1}\\
{\displaystyle y=-\frac{\pi}{2}x-1 - \textrm{asymptota ukośna lewostronna}}\\
{\displaystyle 5. \ \ f'(x)=1\cdot \textrm { arctg }x+x\cdot \frac{1}{1+x^{2}}=\textrm { arctg }x+\frac{x}{1+x^{2}}}\\
\\
{\displaystyle \textrm { arctg }x+\frac{x}{1+x^{2}}=0 }\\
{\displaystyle \textrm { arctg }x=-\frac{x}{1+x^{2}} \ \ \Leftrightarrow \ \ x=0 \ - \textrm{ minimum funkcji }f}
\end{array}\]
\[ \begin{array}{l}
{\displaystyle \textrm { arctg }x \gt -\frac{x}{1+x^{2}} \ \ \Leftrightarrow \ \ x \in \left ( 0; \infty \right ) \ - \textrm{ funkcja rosnąca }}\\
{\displaystyle \textrm { arctg }x\lt -\frac{x}{1+x^{2}}\ \ \Leftrightarrow \ \ x \in \left ( -\infty;0 \right ) \ - \textrm{ funkcja malejąca }}\\
\\
{\displaystyle 6. \ \ f''(x)=\frac{1}{1+x^{2}}+\frac{1(1+x^{2})-x\cdot 2x}{(1+x^{2})^{2}}=\frac{1}{1+x^{2}}+\frac{1+x^{2}-2x^{2}}{(1+x^{2})^{2}}=\frac{1+x^{2}+1-x^{2}}{(1+x^{2})^{2}}=\frac{2}{(1+x^{2})^{2}} \gt 0 \ - \textrm{ funkcja wypukła na całej dziedzinie}}
\end{array}\]