9. (10 points) There are three farms along a road, located at points $A$, $B$, and $C$ as shown in the figure. The farm at $A$ produces 50 tons of wheat annually, the farm at $B$ produces 10 tons of wheat annually, and the farm at $C$ produces 60 tons of wheat annually. A warehouse is to be built along this road to purchase this wheat. Assume the transportation cost from $A$ to $C$ is 1.5 yuan per ton per kilometer, and from $C$ to $A$ is 1 yuan per ton per kilometer. Where should the warehouse be built to minimize transportation costs? At point $P$, find the value of $\frac{\mathrm{EP}}{\mathrm{DP}}$ $\qquad$
【Analysis】Discuss in two cases, that is: (1) Assume a warehouse is established between $A B$; (2) Assume a warehouse is established between $B C$; list the equations and solve them respectively.

【Solution】Solution: (1) Assume a warehouse is established between $A B$, let the distance to $A$ be $x$ kilometers. Then the total cost is: $50 x \times 1.5 + 10 \times (500 - x) \times 1 + 60 \times (1700 - x) \times 1$

Simplifying, we get: $5 x + 107000$
To minimize this total cost,
Since 107000 is fixed, we need to make $5 x$ as small as possible,
So $x=0$, which means setting the warehouse at point $A$ results in the lowest total cost.
(2) Assume a warehouse is established between $B C$, let the distance from point $B$ be $y$ kilometers. Then the total cost is:
$$
50(500 + y) \times 1.5 + 1.5 \times 10 y + 60(1200 - y) \times 1
$$

Simplifying, we get: $109500 + 30 y$,
Similarly, $y=0$, the minimum cost is 109500, which means setting the warehouse at point $B$.
$$
107000 < 109000 \text {. }
$$

In summary, setting the warehouse at point $A$ results in the lowest transportation cost, with the lowest cost being 107000 yuan.
Answer: The warehouse should be built at point $A$ to minimize transportation costs.