Chapter 7 Exponential and Logarithmic Functions - 7.7 Write and Apply Exponential and Power Functions - Guided Practice for Example 4 - Page 531: 8

See below.

Let $y=ax^b$. Then our equations are: $5=a3^b$ and $7=a3^b$. Then from the first equation: $a=\frac{5}{3^b}$. Substituting this into the second equation: $7=\frac{5}{3^b}3^b\\7=5$ This is obviously not true; thus there is no power function that passes through the given points.