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The following sum $$ \sqrt{25-\left(\frac5n\right)^2} \cdot \frac5n + \sqrt{25-\left(\frac{10}n\right)^2} \cdot \frac5n + \cdots + \sqrt{25-\left(\frac{5n}{n} \right)^2} \cdot \frac5n $$ is a right Riemann sum for the definite integral $$\int_a^b f(x)\,\mathrm{d}x$$ where $b = \:\bbox[2px, white, border:1px solid black]{\color{white}{\Rule{5em}{1em}{0.1em}} {\tt 5}}$
and $f(x) = \:\bbox[2px, white, border:1px solid black]{\color{white}{\Rule{1em}{1em}{0.1em}} {\tt sqrt(25 - x^2)}}$.
The limit of these Riemann sums as $n \to \infty$ is  $\bbox[2px, white, border:1px solid black]{\color{white}{\Rule{8em}{1em}{0.1em}}}$ .