Find the sum of first n terms of an appointment a,3a,5a.....
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What's the last term
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First term = a
common difference(d) = 3a - a = 2a
sum of n terms :-
Sn = n/2 ( a + (n-1)d)
Sn = n/2 ( a + (n-1)2a )
Sn = n/2 ( a + 2an - 2a)
Sn = n/2 ( 2an - a)
Sn = an^2 - an/2
Ans. Sn = a (n^2 - n/2 )
common difference(d) = 3a - a = 2a
sum of n terms :-
Sn = n/2 ( a + (n-1)d)
Sn = n/2 ( a + (n-1)2a )
Sn = n/2 ( a + 2an - 2a)
Sn = n/2 ( 2an - a)
Sn = an^2 - an/2
Ans. Sn = a (n^2 - n/2 )
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