Two parallel wires in the plane of the paper are distance X0 apart. A point charge is moving with speed u between the wires in the same plane at a distance $X_{1}$ from one of the wires. When the wires carry current of magnitude I in the same direction, the radius of curvature of the path of the point charge is $R_{1}$. In constrant, if the I in the two wires have directions opposite to each other, the radius of curvature of the path is $R_{2}$. If $X_{1}X_{0} =3$, the value of $R_{2}R_{1} $ is