Find the sum of the series :3+5+7+6+9+12+9+13+17+......to 3n terms
SassyBae:
suno yrr mrudul
nthng.....i was asking about harsh
yeah.....i know yrr.... :'(
but the thing is.....i cant help him out even though i want to
Answers
Answered by
24
GIVEN
3+5+7+6+9+12+9+13+17+.....3n
Where a (first term) = 3
d (common difference) = 5 - 3 = 2
an or L (last term) = 3n
FORMULA
Sn = n / 2 [2a + (n - 1)d]
OR
Sn = n / 2 (a + L)
Sn = n / 2 (3 + 3n)
Sn = (3n / 2) + (3n^2 / 2)
Sn = [ 3n (n + 1)] / 2
3+5+7+6+9+12+9+13+17+.....3n
Where a (first term) = 3
d (common difference) = 5 - 3 = 2
an or L (last term) = 3n
FORMULA
Sn = n / 2 [2a + (n - 1)d]
OR
Sn = n / 2 (a + L)
Sn = n / 2 (3 + 3n)
Sn = (3n / 2) + (3n^2 / 2)
Sn = [ 3n (n + 1)] / 2
but where is the sum
according to the question we have to find the sum of the series
what does this mean^
dear this is the sum.
Answered by
12
the given sequence i.e.,3+5+7+6+9+12+9+13+17+......to3n.
can be written as 3+6+9+....to 10 terms+5+9+13+...to 10terms+7+12+17+....10 terms.
hence the required sum is=10/2
=[2*3+(10-1)3]+10/2
=[2*5+(10-1)4]+10/2
=[2*7+(10-1)5
=5(6+9*3)+5(10+9*4)+5(14+9*5)
=5(6+27+10+36+14+45)
=5*138
=690
can be written as 3+6+9+....to 10 terms+5+9+13+...to 10terms+7+12+17+....10 terms.
hence the required sum is=10/2
=[2*3+(10-1)3]+10/2
=[2*5+(10-1)4]+10/2
=[2*7+(10-1)5
=5(6+9*3)+5(10+9*4)+5(14+9*5)
=5(6+27+10+36+14+45)
=5*138
=690
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