C32 (part 3). The displacement of the medium in a sound wave is given by $y_1 = A\cos(ax + bt)$, where $A$, $a$, $b$ are positive constants. The wave is reflected by an obstacle at $x = 0$. The intensity of the reflected wave is $0.64$ times that of the incident wave. In the resultant wave formed after reflection, the maximum and minimum values of particle speeds in the medium are