Answer
\[\text{The series diverges}\]
Work Step by Step
\[\begin{align}
& \sum\limits_{k=0}^{\infty }{\frac{1}{\sqrt{k+8}}} \\
& \sum\limits_{k=1}^{\infty }{{{a}_{k}}\Rightarrow }\text{ }{{a}_{k}}=\frac{1}{\sqrt{k+8}},\text{ then let }f\left( x \right)=\frac{1}{\sqrt{x+8}} \\
& \text{ }f\left( x \right)=\frac{1}{\sqrt{x+8}}\text{ is continuous and positive for }x\ge 1, \\
& \text{now we will determine if }f\left( x \right)\text{ is decreasing on }\left( 1,\infty \right)\text{, then } \\
& f\left( x \right)=\frac{1}{\sqrt{x+8}} \\
& f\left( x \right)={{\left( x+8 \right)}^{-1/2}} \\
& \text{Differentiating } \\
& f'\left( x \right)=-\frac{1}{2}{{\left( x+8 \right)}^{-3/2}} \\
& \text{Critical point at }x=-8 \\
& \\
& \text{Intervals: }\left( -\infty ,-8 \right)\text{ and }\left( -8,\infty \right) \\
& \text{The domain of the function }f\left( x \right)\text{ is }\left( -8,\infty \right),\text{ then} \\
& \text{*Test for }\left( -8,\infty \right) \\
& f'\left( -7 \right)=-\frac{1}{2}{{\left( -7+8 \right)}^{-3/2}}=-\frac{1}{2}<0 \\
& \text{Therefore}\text{, the function is decreasing for }\left( 1,\infty \right)\text{ } \\
& \text{The function satisfies the conditions for the integral test}\text{.} \\
& \\
& \int_{1}^{\infty }{\frac{1}{\sqrt{x+8}}}dx \\
& \text{Solving improper integral} \\
& \int_{1}^{\infty }{\frac{1}{\sqrt{x+8}}}dx=\underset{b\to \infty }{\mathop{\lim }}\,\int_{1}^{b}{{{\left( x+8 \right)}^{-1/2}}}dx \\
& \text{ }=\underset{b\to \infty }{\mathop{\lim }}\,\left[ {{\left( x+8 \right)}^{1/2}} \right]_{1}^{b} \\
& \text{ }=\underset{b\to \infty }{\mathop{\lim }}\,\left[ \sqrt{b+8} \right]-\underset{b\to \infty }{\mathop{\lim }}\,\left[ \sqrt{1+8} \right] \\
& \text{Evaluate the limit when }b\to \infty \\
& \text{ }=\infty -3 \\
& \text{ }=\infty \\
& \text{The integral diverges}\text{, so by the Integral test }\left( \text{Theorem 8}\text{.10} \right) \\
& \text{The series diverges} \\
\end{align}\]