# If $I_n=\int \limits _0^{\pi/4} \tan ^n \theta d \theta$ for $n=1,2,3........$ then $I_{n-1}+I_{n+1}=.............$

$\begin {array} {1 1} (a)\;0 & \quad (b)\;1 \\ (c)\;\frac{1}{n} & \quad (d)\;\frac{1}{n+1} \end {array}$

$(c)\;\frac{1}{n}$
answered Nov 7, 2013 by