Question

Find the sum of the first 22 terms of the AP: 8,3, -2.......​

Answer 1

Answer:

we already know that our first term is 8

a=8

we do not know our common difference

our common difference will be the second term minus the first term or the third term minus the second term and so on

d= 3-8 =-5 0r    -2-3=-5

d= -5

the sum of N terms = n/2[2a+(n-1)d]

sum of the first 22 terms

22/2(2(8)+(22-1)-5)

11(16+21*-5)

11(16-105)

11(-89)

=-979

therefore the sum of the first 22 terms= -979

Answer 2

Answer:

Your answer starts from here :

8,3,......

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

We know that :

Sn = n/2 { 2a + ( n - 1 ) d }

Therefore,

S₂₂ = 22/2 { 16 + 21 ( - 5 ) }

S₂₂ = 11 ( 16 - 105 )

S₂₂ = 11 ( - 89 )

S₂₂ = - 979

Hence, the sum of first 22 terms of the AP is - 979.