Chapter 4 - Exponential Functions - Exercises to Skills for Chapter 4 - Page 185: 10

$x=\pm 16$

Use the fact that $\sqrt{x}=x^\frac{1}{2}$ and that $(a^b)^n=a^{bn}$ to get the expression $$\sqrt{4^4}=(4^4)^\frac{1}{2}=4^{4(\frac{1}{2})}=4^2=16$$ However, the negative value, $-16$, also works since $(-4^2)(-4^2)=4^4$. Thus, the answers are $\pm 16$.