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find the common difference of an AP whise first term is 1 and the sum of the first four terms is
one -third to the sum of the next four terms
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Answered by
7
a=1
s4=( s8-s4)/3
3 s4= s8- s4
4s4=s8
4×2 (2+3 d)=4 (2+7d)
4+6d=2+7d
d=2
s4=( s8-s4)/3
3 s4= s8- s4
4s4=s8
4×2 (2+3 d)=4 (2+7d)
4+6d=2+7d
d=2
Answered by
6
a = 1. (given)
S4= 1/3*( S8 - S4). (given)
3* S4= S8-S4.
3*S4+S4= S8.
4*S4=S8.
Sn= n/2(2a+(n-1)d). (1)
4*{n/2(2a+(n-1)d)}= n/2(2a+(n-1)d) {Sub (1)}
4*{2(2+3d)}= 4*(2+7d)
4+6d = 2+7d
4-2= 7d-6d
d= 2.
S4= 1/3*( S8 - S4). (given)
3* S4= S8-S4.
3*S4+S4= S8.
4*S4=S8.
Sn= n/2(2a+(n-1)d). (1)
4*{n/2(2a+(n-1)d)}= n/2(2a+(n-1)d) {Sub (1)}
4*{2(2+3d)}= 4*(2+7d)
4+6d = 2+7d
4-2= 7d-6d
d= 2.
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