Arithmetic Series (Edexcel A-Level Mathematics): Flashcards

It means adding all terms in a sequence together.

$u_n = a + (n-1)d$

$S_n = \frac{n}{2}[2a + (n-1)d]$

$S_3 = 1 + 7 + 13 = 21$

$a$ is the first term; $d$ is the common difference.

Rearrange to $a = 72 - 2d$, using known $d$ value.

$l$ is the value at $n = 59$, which is $355$.

It's an efficient way to sum with known first and last terms.

It is an arithmetic sequence.

Set up and solve the equation $S_N = 2200$.