Resistance and Capacitators - check my work.

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vucollegeguy
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A heart pacemaker is designed to operate at 71 beats/min using a 8.5 microF 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 69% of maximum?

Here's what I've done (but my answer was wrong):

R= t / (C*ln[v0 / v])

with t = 1.183 beats/sec
C = 8.5 x 10-6F
v0/v = 0.69

R = -3.8 x 108 ohms

Where did I go wrong?
 
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