6. Two flagpoles of heights 5 meters and 3 meters are erected on a level ground. If the coordinates of the bottoms of the two flagpoles are determined as $A(-5,0)$ and $B(5,0)$, then the locus of points on the ground where the angles of elevation to the tops of the poles are equal is $\qquad$ .
6. $\left(x-\frac{85}{8}\right)^{2}+y^{2}=\left(\frac{75}{8}\right)^{2}$. Hint: The ratio of the distances from the points on the ground where the angles of elevation to the tops of the poles are equal is equal to the ratio of the heights of the two poles.