# How do you determine if the equation y= 90 (0.5)^x represents exponential growth or decay?

To know whether $y = 90 {\left(0.5\right)}^{x}$ represents exponential growth or decay, you must look at the rate (or the $b$ value in $y = a {\left(b\right)}^{x}$.
If the $b$ value is between 0 and 1 then it is an exponential decay.
If the $b$ value is greater than 1 then it is an exponential growth.
Looking that the $b$ value for the function presented above, it shows that it's an exponential decay because 0.5 is between 0 and 1.