Arithmetic Series (Edexcel A-Level Mathematics): Quizzes

Adding all terms in a sequence together

Sum of first $n$ terms of a series

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

$21$

$a+2d=72$ and $a+7d=37$

Using $S_{59} - S_{21}$

$39$

Last term being summed

$u_1=7$, $u_2=9$

$44$