Q1 of 67 Page 74

Find the sum of the following arithmetic progressions:

8, 3, -2, … upto 22 terms.

The arithmetic progression 8, 3, -2, …. is given.
Here first term is 8 and common difference is 3 – 8 = -5.
Since the sum of n terms is
Sn =


Where,


a = First term of AP
d = Common difference of AP
and no of terms is ‘n’



So sum of first 22 terms S22
]
= 11[ 16 + 21×(-5)]
= 11[16 - 105]
= 11 × (-89)
= -979


Hence, Sum of first 22 terms is -979.


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