Wolfram Alpha != HP Prime CAS result: who is wrong?

[Thomas Klemm]

(06-04-2024 01:08 AM)robve Wrote:  \( \sum_{k=0}^n=\frac12n(n+1) \)
but it also says that:
\( \sum_{k=0}^{-10}=0 \)

You missed the \(k\) in your sums:

\(
\begin{align}
\sum_{k=0}^n k &=\frac{1}{2} n(n+1) \\
\\
\sum_{k=0}^{-10} k &=0 \\
\end{align}
\)