AP: sum of first n terms (S_n = n/2 * (2a + (n-1)d) = n/2 * (a + l))
jee-mainjee-advanced
S_n = n/2 * (2a + (n-1)d) = n/2 * (a + l)
What each symbol means
| Symbol | What it stands for |
|---|---|
| a | First term |
| d | Common difference |
| l | Last term a_n |
| n | Number of terms |
| S_n | Sum of first n terms |
When to use this
n is count of terms summed.