[填空题]
A heart pacemaker is desigp7nrp2d) o/uo ned.qe6-jrw 7s q ha)wlr) to operate at 72 beats/min using a $7.5-\mu F$ capacitor in a simple RC circuit. What value of resistance should be used if the pacemaker is to fire (capacitor discharge) when the voltage reaches 63% of maximum? $ \times10^{-5 }\;\Omega$
