calculus---optimization

A company has plants that are located (in an appropriate coordinate system) at the points A(0,1), B(0,-1) and C(3,0). The company plans to construct a distribution center at the point P (x,0), where x is positive. What value of x would minimize the sum of the distances from P to A, B, and C?

Ans: P(1/square root 3, 0)