A tower, of x meters high, has a flagstaff at its top. The tower and the flagstaff subtend equal angles at a point distant y meters from the foot of the tower. Then the length of the flagstaff(in meters), is :

Question

$$\begin {array} {1 1} (a)\;\frac{y(x^2-y^2)}{(x^2+y^2)} & \quad (b)\;\frac{x(y^2+x^2)}{(y^2-x^2)} \\ (c)\;\frac{x(x^2+y^2)}{(x^2-y^2)} & \quad (d)\;\frac{x(x^2-y^2)}{(x^2+y^2)} \end {array}$$