SEQUENCES Sums (Page 3 of 7)

The sum command can also be used to find a partial sum for a sequence, as long as we begin the sum with the first term. Let's find the twentieth partial sum for the sequence a(subscript n) = (1/2)n(n+1), which will be the sum of terms 1 through 20.

 CLEAR key.

 2nd LIST key. [MATH] 5: menu selection. 2nd LIST key. [OPS] 5: menu selection. ALPHA N key. Left parenthesis key. ALPHA N key. Plus key. 1
 Right parenthesis key. Divide key. 2 Comma key. ALPHA N key. Comma key. 1 Comma key. 20 Right parenthesis key. Right parenthesis key. ENTER key.

 Calculator screen image.

Notice we began the sum with the first term and ended the sum with the twentieth term.
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