Question

Find the sum of the first 22 terms of the AP:8;3 -2

Answer 1

a = 8 , d = 3 - 8 = -5 , n = 22
sn = n/2(2a + (n-1)(d) )
s22 = 22/2 (2(8) + (22-1)(-5) )
s22 = 11 ( 16 + (21)(-5) )
s22 = 11 ( 16 - 105 )
s22 = 11( -89 )
s22 = -979
Sum of the first 22 terms of this AP is -979.

Answer 2

Sn=n/2(2a+(n-1)×d)
Sn=11 (16+(21)×-5)
Sn=11 (16-105)
Sn=11 (-89)
Sn=_979
Sn=979