How do you tell if something is a exponential decay or not?

Question

anonymous · Answer

If the amount that it decays per second is a function of how much stuff there is at that moment, then it can be expressed as E.D.

campbell_st · Answer

got exponential growth... the constant k is positive, for decay its negative

growth model

$$A = Pe^{kt}$$

decay model

$$A=Pe^{-kt}$$

hope this helps

anonymous · Answer

But if you are given$$A=Pb ^{kt}$$ where b is a constant, you can convert it into$$A=Pe ^{kt}$$

campbell_st · Answer

the other test to see if it is exponential is to differentiate and seek that the derivative is a proportional to the model

e.g for the growth model

$$A=Pe^{kt}$$

$$\frac{dA}{dt} = kPe^{kt}$$

which can be written in terms of the original model 

$$\frac{dA}{dt} = k(Pe^{kt}) = kA$$

anonymous · Answer

still confused but ill youtube it thanx guys

anonymous · Answer

http://www.youtube.com/watch?v=HTDop6eEsaA He's always good

anonymous · Answer

if b is greater than 0 but less than 1, then it is decay....

anonymous · Answer

because.. b^k = (1/b)^(-k).  so if 0<b<1, the equation will be a decay.

anonymous · Answer

still need help?

anonymous · Answer

It will also decay (no matter what b is) if k is negative.