Which exponential function goes through the points (1,8) and (4,64)?

a) f(x)=4(2)^x

b) f(x)=2(4)^x

c) f(x)=4(2)^-x

d) f(x)=2(4)-x

Plug in (4,64) into each answer choice.

A) 4(2)^x
64 =4(2)^4 
64 = 4(16) 
64 = 64

Answer choice A is correct.

B) f(x) = 2(4)^x
64 = 2(4)^4
64 = 2(256)
64 ≠ 512

Answer choice B is incorrect.

C) f(x) = 4(2)^{-x}
64 = 4(2)^{-4}
64 = 4(-0.0625)
64 ≠ 0.25

Answer choice C is incorrect.

D) f(x) = 2(4)^{-x}
64 = 2(4)^{-4}
64 = 2(0.00390625)
64 ≠ 0.0078125

Answer choice D is incorrect.

Your answer is B) f(x)=2(4)^x