For `nge 2, " let "a_(n)=Sigma_(r=0)^(n) (1)/(C_(r)^(2))`, then value of `b_(n)=Sigma_(r=1)^(n) (1)/(r^(2)C_(r)^(2))` equals……(where `C_(r)` denotes `""^(n)C_(r)`).

Options

A. `(1)/(n^(2))a_(n)`
B. `(1)/(n^(2))a_(n-1)`
C. `a_(n)`
D. `a_(n)^(2)`

Answer

A

Explanation

`R_(3)rarrR_(3)cosbetaR_(1)+sinbetaR_(2)`
`f(alpha,beta)=|{:(cosalpha,-sinalpha,," "1,),(sinalpha,cosalpha,," "1,),(0," "0,,1-cosbeta+sinbeta,):}|=1-cosbeta+sinbeta`