What are exponential growth and exponential decay?

• y = Ae^kt?is exponential?growth

• y = Ae^-kt?is exponential?decay

• k > 0?so plus or minus sign in equation immediately indicates growth or decay
• A?is the?starting?value or?initial?value, when?t = 0
• t?is often used, rather than?x, as many models are time-dependent

Is e always used in exponential growth and decay?

• Using?e?makes the maths easier
• With the proper choice of?k, all exponential functions of the form?a^x?can be written in the form?e^kx
  • a^x?= e^kx

Will logarithms or ln be involved?

• ln?is the inverse of?e

• The graph of?y = ln?x?is the reflection of the graph of?y = e^x?in the line?y = x