# How do you determine if the equation y= 0.5 (0.9)^x represents exponential growth or decay?

Anything to the $x$ will be growth, if it's ${n}^{\textcolor{red}{-} x}$ then it'll be decay.
${n}^{- x} = \frac{1}{n} ^ x$
Therefore as $x$ increases, $y$ will decrease.
When you have ${n}^{x}$ as $x$ increases so will $y$.