Question

find the sum of first 22 terms of the A.P 8,3,-2,-7...........

Answer 1

a=8,
d=3-8=-5
n=22

s=n/2[2a+(n-1)]

s= 22/2(16+21-5)

s=11(16-105)

s=11(-89)

s=-979

Answer 2

Answer:

-979

Step-by-step explanation:

AP : 8, 3, - 2, - 7,....., to 22 terms.

Here, we have ;

First term (a) = 8

Number of terms (n) = 22

Difference (d) = 3 - 8 = -5

Sum of n terms is given by formula :

$\bf S_n = \frac{n}{2}[2a +(n-1)d] \\ \\ \bf S_{22} = \frac{22}{2}[2 \times 8+(22-1)(-5) ] \\ \\ \bf S_{22} = 11[16 + 21 \times (-5)] \\ \\ \bf S_{22}= 11[ 16 - 105] \\ \\ \bf S_{22}= 11 \times (-89)\\ \\ \red{\boxed{\bf S_{22} = - 979}}$

Hence, the sum of the given AP is -979.