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Sum of Nth Term

Asked: 10 months ago

Find the sum the first 25th terms of following series:

2,5,8,11,14,⋯

Formula to find nth term:

Formula to find sum of n terms:

Solution


# First find the 40 th term:
a40 = a1+(n−1)d
    = 2+39(3)
    = 119

# Then find the sum:
Sn = n(a1+an)/2
   = 40(2+119)/ 2
   = 2420    
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