find the sum of first n terms of an ap whose n term is 5 n -1 also find is 20 term
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given Tn = 5n-1
for sum of nth term we will apply sigma on Tn
Sn= sigma (5n-1)
=( 5(n)(n+1)/2) -n
for sum of 20 term put n = 20 in sn
= (5*20*21/2)-20
= 1030
and for 20 th term put n = 20 in tn
= 5*20-1 = 99
for sum of nth term we will apply sigma on Tn
Sn= sigma (5n-1)
=( 5(n)(n+1)/2) -n
for sum of 20 term put n = 20 in sn
= (5*20*21/2)-20
= 1030
and for 20 th term put n = 20 in tn
= 5*20-1 = 99
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