A..b two villages are on the same side of the river CD, and the distances to the river are AC= 1KM, BD=3KM and CD=3KM respectively. First of all, a water plant should be built on the CD by the river t

A..b two villages are on the same side of the river CD, and the distances to the river are AC= 1KM, BD=3KM and CD=3KM respectively. First of all, a water plant should be built on the CD by the river to transport water to two villages. Use CD as the mirror point of A', the focal point connecting A'B, A' B and CD is O, and the shortest distance is A' b..

So a 'b2 = 3 2+(1+3) 2 Pythagorean Theorem

So a' b = 5 kilometers.

So the minimum cost is 5×2 = 65438+ ten thousand yuan.