Two parallel wires in the plane of the paper are distance $X_0$ 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 contrast, if the currents I in the two wires have direction opposite to each other, the radius of curvature of the path is $R_2$. If $\frac{x_0}{x_1}=3$, the value of $\frac{R_1}{R_2}$ is.