express the sequence {0,...,0,-1,-1,-1,-1,0(origin),0,0,0...,0} in terms of

a. scaled/shifted impulses

is the answer

$\displaystyle x(n) = -\sigma(n+1)-\sigma(n+2)-\sigma(n+3)-\sigma(n+4)? $

b. unit step function

is the answer

x(n) = -u(-(n+5))-u(-n)?