make pdf file generation work
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@@ -534,9 +534,20 @@ http://www.ams.org/samplings/feature-column/fc-2016-05.)
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"""
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ImageFile(:derivatives, imgfile, caption)
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#ImageFile(:derivatives, imgfile, caption)
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nothing
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```
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The last example is a modern day illustration of a problem of calculus dating back to l'Hospital. His parameterization is a bit different. Let's change his by taking two points $(0, a)$ and $(L,-b)$, with $a,b,L$ positive values. Above the $x$ axis travel happens at rate $r_0$, and below, travel happens at rate $r_1$, again, both positive. What value $x$ in $[0,L]$ will minimize the total travel time?
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@@ -1227,9 +1238,13 @@ caption = L"""
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Image number $40$ from l'Hospital's calculus book (the first calculus book). Among all the cones that can be inscribed in a sphere, determine which one has the largest lateral area. (From http://www.ams.org/samplings/feature-column/fc-2016-05)
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"""
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ImageFile(:derivatives, imgfile, caption)
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#ImageFile(:derivatives, imgfile, caption)
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nothing
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```
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).](./figures/fcarc-may2016-fig40-300.png)
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The figure above poses a problem about cones in spheres, which can be reduced to a two-dimensional problem. Take a sphere of radius $r=1$, and imagine a secant line of length $l$ connecting $(-r, 0)$ to another point $(x,y)$ with $y>0$. Rotating that line around the $x$ axis produces a cone and its lateral surface is given by $SA=\pi \cdot y \cdot l$. Write $SA$ as a function of $x$ and solve.
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@@ -1345,12 +1360,12 @@ solve(x/b ~ (x+a)/(b + b*p), x)
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With $x = a/p$ we get by Pythagorean's theorem that
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$$
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\begin{align*}
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c^2 &= (a + a/p)^2 + (b + bp)^2 \\
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&= a^2(1 + \frac{1}{p})^2 + b^2(1+p)^2.
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\end{align*}
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$$
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The ladder problem minimizes $c$ or equivalently $c^2$.
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