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\newenvironment{esim}{\Large {\color{red}\textbf{Esimerkki.}} \color{blue}}{\color{red}$\square$}

\begin{document}

\begin{esim}
Funktion $f:\R^2 \rightarrow \R^3$, $(x,y,z) = f(\theta,\phi)$, missä
\[
\left\{\begin{aligned}
x &= \sin\theta\cos\phi,\\ y &= \sin\theta\sin\phi,\\ z &= \cos\theta,
\end{aligned}\right.
\]
Jacobi'n matriisi $\J_f$ on
\[
\J_f(\theta,\phi) =
\begin{pmatrix}
\Osder{x}{\theta} & \Osder{x}{\phi} \\[20pt]
\Osder{y}{\theta} & \Osder{y}{\phi} \\[20pt]
\Osder{z}{\theta} & \Osder{z}{\phi}
\end{pmatrix} =
\begin{pmatrix}
\cos\theta\cos\phi & -\sin\theta\sin\phi \\
\cos\theta\sin\phi & \sin\theta\cos\phi \\
-\sin\theta & 0
\end{pmatrix}.
\]
\end{esim}

\end{document}
