Question

14.Find the sum of the first 22 terms of the AP : 8, 3, –2, . . .

Answer 1

Answer:  $S_{22} = 979$

Step-by-step explanation:

A.P. = 8 , 3 , -2 , .....

first term = a = 8, common difference = d => $a_{2} -a_{1}$ => 3 - 8 => 5 = d

number of terms => 22 = n

we know that sum of " n " terms =>    $S_{n} = \frac{n}{2} [2a+(n-1)d]$

$S_{22} = \frac{22}{2} [2*8+(22-1)(-5)]$

$S_{22} = 11 [16+(21)(-5)]$

$S_{22} = 11 [16-105]$

$S_{22} = 11 [89]$                       { There is modulus so -89 becomes +89 }

$S_{22} = 979$