Question 1207740
<pre>
{{{system(a - b = 4,a^2 - b^2 = 8)}}}

{{{a=b+4}}}

{{{(b+4)^2-b^2=8}}}

{{{b^2+8b+16-b^2=8}}}
{{{8b+16=8}}}
{{{b+2=1}}}
{{{b=-1}}}
{{{a=b+4}}}
{{{a=-1+4}}}
{{{a=3}}}

Since 
(c) the only possible values of a and b are 3 and -1, respectively, then
(a) the only possible value for ab is (3)(-1) = -3, and
(b) the only possible value for a+b is (3)+(-1) = 2.

Edwin</pre>