Chapter 7 Exponential and Logarithmic Functions - 7.7 Write and Apply Exponential and Power Functions - Guided Practice for Examples 1, 2, and 3 - Page 531: 3

$y=2^x$

Let $y=ab^x$. Then our equations are: $8=ab^3$ and $64=ab^6$. If we divide the second equation by the first one we get: $8=b^3$. thus because $b$ is positive: $b=2$. Then $8=a\cdot2^3=8a\\a=1$. Thus $y=1\cdot2^x=2^x$