Find a possible formula for the exponential function through the points (−2,100) and (1,4/5)

100 = ab^(-2)      ⇒ 100 =  a / b^2   (1)

.8 = ab^1    ⇒  .8 = ab   ⇒  .8/b  = a   (2)

Sub (2) into (1)  for a

100 =  .8 / b^3

b^3 =  .8/100

b^3 = (8/10)(1/100)

b^3  = 8/1000

b =  2 /10  =  .2

And

.8/.2 = a  = 4

So....the function is

y = 4(.2)^x