In a ap the sum of first n term is 5n^2/2+3n/2 find its 20th terms
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Given,
Sn = 5n^2/2 +3n/2
Put n = 1
S1 = a =5/2+3/2
=4
Put n= 2
S2 = 20/2+6/2 = 13
Put n = 3
S3 = 45/2+9/2
= 27
a = 4
a2= S2-S1
=13-4
=9
a3 = S3-S2
=27-13
=14
So the AP is
4,9,14,.......
d=a2-a
=9-4 = 5
We have to find the 20th term i.e. a20
a20 = a+19d
=4+19×5
=99
HOPE IT HELPS
Sn = 5n^2/2 +3n/2
Put n = 1
S1 = a =5/2+3/2
=4
Put n= 2
S2 = 20/2+6/2 = 13
Put n = 3
S3 = 45/2+9/2
= 27
a = 4
a2= S2-S1
=13-4
=9
a3 = S3-S2
=27-13
=14
So the AP is
4,9,14,.......
d=a2-a
=9-4 = 5
We have to find the 20th term i.e. a20
a20 = a+19d
=4+19×5
=99
HOPE IT HELPS
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