What the forget? y = nr2 -2nr + n is not the equation for exponential decay. Exponential decay is y = a*bx where 0 < b < 1.
then what the forget were we doing then because that's how we were solving the decay problems
y = nr2 -2nr + n
wait wait wait where are you getting this
we solve the problems by being given a starting number and a percent, put the starting number for the n and then putting the percent in a decimal. so it'd be like
y=4000(1-.045)
ty=4000(.955)
ty=3381.49
atleast that's how i think it works, i'll have to look at my notes again to make sure