Question 80212
Find the half-life of a radioactive element that decays according to the rule: 
dA/dt=-0.014A
where A is the amount in kg present after t years.
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Integrating you get A(t)=-0.014At
If A is doubled you have:
2A=-0.014At
2=-0.014t
t=2/-0.014
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Comment:
This would give you a negative value for t.
I think something is missing in your posting.
Decay functions are exponential.  Your posting
does not lead to that conclusion.
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Cheers,
Stan H.