Question 23331
To do this problem, think about the quadratic {{{a^2+2a-15}}}.  Where is this quadratic zero?  Note that the quadratic factors to (a-3)(a+5), so it is zero when a = 3 and when a = -5.

Now when is the quadratic bigger than zero?  To solve this, think about graphing the quadratic.

{{{ graph( 300, 200, -8, 4, -10, 10, x^2+2x-15) }}}

The graph tells us that it is bigger than zero when x [or in our case, a] is less than -5 or greater than 3.

So the solution to this is {{{x>=-5}}} or {{{x<=3}}}