<<echo=FALSE, results=hide>>=
p <- c(sample(1:3, 1), sample(1:5, 1))
q <- c(sample(4:5, 1), sample(1:5, 1))
sol <- sqrt(sum((p - q)^2))
@

\begin{question}
What is the distance between the two points
$p = (\Sexpr{p[1]}, \Sexpr{p[2]})$ and $q = (\Sexpr{q[1]}, \Sexpr{q[2]})$
in a Cartesian coordinate system?
\end{question}

\begin{solution}
The distance $d$ of $p$ and $q$ is given by
$d^2 = (p_1 - q_1)^2 + (p_2 - q_2)^2$ (Pythagorean formula).

Hence $d = \sqrt{(p_1 - q_1)^2 + (p_2 - q_2)^2} =
  \sqrt{(\Sexpr{p[1]} - \Sexpr{q[1]})^2 + (\Sexpr{p[2]} - \Sexpr{q[2]})^2}
   = \Sexpr{round(sol, digits = 3)}$.

<<echo=FALSE, results=hide, fig=TRUE>>=
par(mar = c(4, 4, 1, 1))
plot(0, type = "n", xlim = c(0, 6), ylim = c(0, 6), xlab = "x", ylab = "y")
grid(col = "slategray")
points(rbind(p, q), pch = 19)
text(rbind(p, q), c("p", "q"), pos = c(2, 4))
lines(rbind(p, q))
lines(c(p[1], p[1], q[1]), c(p[2], q[2], q[2]), lty = 2)
@
\end{solution}

%% \extype{num}
%% \exsolution{\Sexpr{round(sol, digits = 3)}}
%% \exname{Euclidean distance}
%% \extol{0.01}