



 
Aisyah, Since dA/dt = kA you have dA/A = k dt. A is a function of t so if you integrate both sides you get
where C is a constant. Take the exponential of both sides to obtain
When t = 0 this gives
But you were told that A(0) = A so
The half life is the time T when A(T) = 1/2 A(0) = 1/2 A. Solve for T. I hope this helps,  


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