What's the value of f(-2)?

Question

An exponential function is given in the form f(x)-a*b^x. If f(0)=3 and f(1)=15, what's the value of f(-2)?

Answer 1

 

f(0) = 3 = a*b⁰  Therefore 3 = a (1) 

 

f(1) = ab = 15 

 

3b =15 

 

b =5 

 

a =3 b =5 

 

f(-2) = 3.5^-2 = 3/25 

Answer 2

f(x) = ab^x

f(0) = ab⁰ = a(1) = a = 3 (given)

f(1) = 3b¹ = 3b = 15 ⇒ b = 5

f(-1) = 3•5^-1 = 3/25.