The solution and the answer in the post by @mananth both are incorrect.
I came to bring a correct solution.
This request is to solve inequality
x^2 + 8x + 15 >= 0.
Left side can be factored
(x+5)*(x+3) >= 0.
The solution for this inequality is the union of two sets of real numbers
x <= -5 OR x >= -3.
In the interval form, the solution is (,] U [,).
