Directly Proportional (or just proportional)

• If a is proportional to b, then a=kb

Inversely Proportional (or proportional to the reciprocal)

• If a is inversely proportional to b, then a=k/b

Exponential Function

• Quantities that changes by a factor/percentage at regular interval are exponential.

<aside> 💡 The rate of change of the quantities is proportional to itself or mathematically: $\frac {dy} {dxt}=ky$ where k is not equal to zero.

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• If $\frac {dy} {dt}=ky$ then $Ce^{kt}$, where C is the initial amount present (y intercept)