Q1 of 67 Page 74

Find the sum of the following arithmetic progressions:

1, 3, 5, 7, …. upto 12 terms

The arithmetic progression 1, 3, 5, 7, …. is given.
Here first term is 1 and common difference is 3 – 1 = 2.
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 12 terms S12
= 6[ 2 + 11×2]
= 6[2 + 22]
= 6 × 24
= 144


Hence, Sum of first 12 terms is 144.


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