`underset(nrarroo)limunderset(r=1)overset(n)Sigma(r)/(1xx3xx5xx7xx9xx...xx(2r+1))` is equal to

lim_(nrarroo) Sigma_(r=1)^(n) (r)/(1xx3xx5xx7xx9xx...xx(2r+1)) is equal to

If Sigma_(r=1)^(n) r^4=I(n), " then "Sigma__(r=1)^(n) (2r -1)^4 is equal to

1+1/3x+(1xx4)/(3xx6)x^2+(1xx4xx7)/(3xx6xx9)x^3+ .... is equal to

1+1/4 + (1xx3)/(4xx8) + (1xx3xx5)/(4xx8xx12) + "….." is equal to

Find the sum Sigma_(j=1)^(n) Sigma_(i=1)^(n) I xx 3^j

Find the sum of infinite series (1)/(1xx3xx5)+(1)/(3xx5xx7)+(1)/(5xx7xx9)+….

If (1+i)(1+2i)(1+3i)"……."(1+ni)=a+ib," then "2xx5xx10xx"………"xx(1+n^2) is equal to

Find the sum 1-1/8+1/8xx3/(16)-(1xx3xx5)/(8xx16xx24)+

If overset(to)(a) , overset(to)(b) , overset(to)(c ) " and " overset(to)(d) are the unit vectors such that (overset(to)(a)xx overset(to)(b)). (overset(to)(c )xx overset(to)(d)) =1 " and " overset(to)(a), overset(to)(c ) = .(1)/(2) , then