Calculus - Minimizing Distance

Calculus Level 3

A power house, P, is on one bank of a straight river 200 m wide, and a factory, F, is on the opposite bank 400m downstream from P. The cable has to be taken across the river, under water at a cost of $6/m. On land the cost is$3/m. Tell the least cost with shortest angle?

NOTE: path should be chosen so that the cost is minimized

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