# A Controlled Spiral

Calculus Level 3

Suppose a particle moves in a right-angled left spiral on an $$xy$$-grid. That is, it moves a distance $$D_{1}(x)$$ in a straight line, stops, makes a right-angled turn to it's "left", travels a distance $$D_{2}(x)$$ in a straight line, stops, makes a right angled turn to its "left", travels a distance $$D_{3}(x)$$ in a straight line and continues in this fashion forever.

If $$D_{n}(x) = \dfrac{x^{n-1}}{(n-1)!}$$ for $$n \ge 1,$$ and if $$x = 2015,$$ then find the magnitude of the straight line distance between the particle's starting and finishing points.

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