Replace the right hand sides of [math]x_1\left(t\right)[/math], [math]y_1\left(t\right)[/math], [math]x_2\left(t\right)[/math], and [math]y_2\left(t\right)[/math]so that [math]P_1[/math] starts on the positive [i]x[/i]-axis and moves along the circle counterclockwise, while [math]P_2[/math] starts on the positive [i]y[/i]-axis and moves along the circle clockwise.