what is the formula for finding sum of n terms of G.P.Is it a*(1-r n )/(1-r) or a*(r n -1)/(r-1). I am confused.My teacher says it is same, but its not same.
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you are write but your sir is also not wrong .
let a example :-
you have given a series,
1, 1/2,1/4,1/8 .........
here you see ,
r=1/2 hence r is less then 1
hence here you can you use both but
mathematically correct use of
Sn=a(1-r^n)/(1-r)
in the way condition when common ratio (r) greater than 1 then you use other one .
but generally both are same because if we solve both way result are always same .so, don't confuse ,frequently use both way but sign must convenience.
let a example :-
you have given a series,
1, 1/2,1/4,1/8 .........
here you see ,
r=1/2 hence r is less then 1
hence here you can you use both but
mathematically correct use of
Sn=a(1-r^n)/(1-r)
in the way condition when common ratio (r) greater than 1 then you use other one .
but generally both are same because if we solve both way result are always same .so, don't confuse ,frequently use both way but sign must convenience.
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