## Algebra 1

To find the initial amount, plug 0 in for x: y = 0.1 (0.9)$^{x}$ y = 0.1 (0.9)$^{0}$ y = 0.1 (1) y = 0.1 0.9 is the decay factor because this is the value that is attached to the "x" exponent. In other words, this is the value that will determine by how much x decays.