if 6th terms of an A.P.is 121 then find the sum of its firest 11 terms.
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Answered by
8
a+5d=121
let a=1
1+5d=121
5d=120
d=24
a+5*24=121
a+120=121
a=1 ------------------------------------------(i)
s11=11/2(2*1+10*24)
s11=11/2(2+240)
s11=11/2*242
s11=11*121
s11=1331 ANS
let a=1
1+5d=121
5d=120
d=24
a+5*24=121
a+120=121
a=1 ------------------------------------------(i)
s11=11/2(2*1+10*24)
s11=11/2(2+240)
s11=11/2*242
s11=11*121
s11=1331 ANS
tarakahuja123:
but after it i proved that a =1 form eq (i)
Answered by
3
x6=121
sn=n*center term(this is a formula to find the sum of an A.P if it's number is an odd)
=11*121=1331
sn=n*center term(this is a formula to find the sum of an A.P if it's number is an odd)
=11*121=1331
SRY N=6
n= total number of the terms ...so it is 11
but then sn= n/2 (2a+(n-1)d)
this is an other formula
can u pls tell me this formula in detail ls i have xam tommrow
if the n is an odd number we can use this formula. n*center term
in my ans why we cant take a=1
but yur formula is not given on internet even
you can use it in any question if n isodd
pls answer this also http://brainly.in/question/79378
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