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# If $(1+x+x^2+x^3)^5= \sum \limits_{k=0} ^{15} a_k x^k$ then $\sum \limits_{k=0}^7 a_{2k}=$

$\begin {array} {1 1} (1)\;128 & \quad (2)\;256 \\ (3)\;512 & \quad (4)\;1024 \end {array}$

Can you answer this question?

(3) 512
answered Nov 7, 2013 by