Answer: D) construct the circumcenter
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Step-by-step explanation:
Consider triangle ABC. The vertex points are at A,B,C. These represent the three cities in which the three different daughters live. Constructing the circumcenter will produce a circle such that all three points A,B,C are on that circle. Let's say that D is the center of that circle.
This means that AD, BD, CD are all radii of this same circle. Radii of the same circle are the same length, which is why point D is equally distant from A,B,C. If the mother lives at point D, then she will travel the same distance to visit any three of her daughters. See the note below.
To construct the circumcenter, we form perpendicular bisectors to segments AB, BC and AC. Technically you only need two of them. All three of these perpendicular bisectors intersect at point D.
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Note: Keep in mind that roads aren't completely straight, so that means we'll have to factor in the curvature of each road. But to keep things simple, we assume each road is a straight line segment.