Question 638733
For excluded values look at denominators and square roots.  Values that make the denominator 0 or square roots - are excluded.  In this case a=-7 makes the denominator 0.  So a=-7 is excluded.<P>
Factor the top:  {{{a^2+16a+63 = (a+7)(a+9)}}}.<P>
{{{(a+7)(a+9) / (a+7) }}} The (a+7) terms cancel.  The simplified version is a+9.