Type sum to get Σ. Fill in the start, the end, and the formula in n. Desmos adds the series. Arithmetic sums by hand are in arithmetic series sum.
Index, then the formula
Σ from n = 1 to 10 of n² is a keypad job, not ten squares on scratch paper. Permutations and combinations are a different leftover, in nPr and nCr.
Desmos as a tool is in Desmos on the ACT.
The bottom line
Type sum. Fill start, end, and formula. Let Σ add.
Start practicing
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