```{r data generation, echo = FALSE, results = "hide"}
sc <- NULL
while(is.null(sc)) {
## parameters
a <- sample(2:9, 1)
b <- sample(seq(2, 4, 0.1), 1)
c <- sample(seq(0.6, 0.9, 0.01), 1)
## solution
res <- exp(b * c) * (a * c^(a-1) + b * c^a)
## schoice
err <- c(a * c^(a-1) * exp(b * c), a * c^(a-1) * exp(b * c) + c^a * exp(b * c))
rg <- if(res < 4) c(0.5, 5.5) else res * c(0.5, 1.5)
sc <- num_to_schoice(res, wrong = err, range = rg, delta = 0.1)
}
```

Question
========
What is the derivative of $f(x) = x^{`r a`} e^{`r b` x}$, evaluated at $x = `r c`$?

```{r questionlist, echo = FALSE, results = "asis"}
answerlist(sc$questions, markup = "markdown")
```

Solution
========
Using the product rule for $f(x) = g(x) \cdot h(x)$, where $g(x) := x^{`r a`}$ and $h(x) := e^{`r b` x}$, we obtain
$$
\begin{aligned}
f'(x) &= [g(x) \cdot h(x)]' = g'(x) \cdot h(x) + g(x) \cdot h'(x) \\
      &= `r a` x^{`r a` - 1} \cdot e^{`r b` x} + x^{`r a`} \cdot e^{`r b` x} \cdot `r b` \\
      &= e^{`r b` x} \cdot(`r a` x^`r a-1` + `r b` x^{`r a`}) \\
      &= e^{`r b` x} \cdot x^`r a-1` \cdot (`r a` + `r b` x).
\end{aligned}
$$
Evaluated at $x = `r c`$, the answer is
$$ e^{`r b` \cdot `r c`} \cdot `r c`^`r a-1` \cdot (`r a` + `r b` \cdot `r c`) = `r fmt(res, 6)`. $$
Thus, rounded to two digits we have $f'(`r c`) = `r fmt(res)`$.

```{r solutionlist, echo = FALSE, results = "asis"}
answerlist(ifelse(sc$solutions, "True", "False"), markup = "markdown")
```

Meta-information
================
extype: schoice
exsolution: `r mchoice2string(sc$solutions)`
exname: derivative exp