Sum of first n terms of an AP (Sum is half the number of terms times first plus last)
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Sum is half the number of terms times first plus last
What each symbol means
| Symbol | What it stands for |
|---|---|
| l | Last term a_n |
| S_n | Sum of first n terms |
| a,d,n | As in AP |
When to use this
Valid for any AP; l = a + (n−1)d.