Question 1150620
<pre>8+6+4+2+0+(-2)+(-4)+(-6)+(-8)+(-10)+(-12)+(-14)+(-16)+(-18)+(-20)+(-22)+(-24)+(-26)+(-28)+(-30)+(-32) = -252

By formula, where a<sub>1</sub> = first term, a<sub>n</sub> = nth term, 
n = number of term(s), d = common difference between any term after the first,
and the preceding term.  S<sub>n</sub> = sum of first n terms.

{{{matrix(1,3,a[n],""="",a[1]+(n-1)d))}}}
{{{matrix(1,3,-32,""="",8+(n-1)(-2))}}}
{{{matrix(1,3,-32,""="",8+(-2)(n-1))}}}
{{{matrix(1,3,-32,""="",8+(-2n+2))}}}
{{{matrix(1,3,-32,""="",8-2n+2)}}}
{{{matrix(1,3,-32,""="",10-2n)}}}
{{{matrix(1,3,-42,""="",-2n)}}}
  {{{matrix(1,3,21,""="",n)}}}


{{{matrix(1,3,S[n],""="",expr(n/2)(a[1]+a[n]))}}}
{{{matrix(1,3,S[21],""="",expr(21/2)(8+(-32)^""))}}}
{{{matrix(1,3,S[21],""="",expr(21/2)(-24))}}}
{{{matrix(1,3,S[21],""="",-252)}}}

Edwin</pre>