x^2 + 2x < 8
x^2 + 2x - 8 < 0
(x + 4)(x - 2) < 0 ,,
{x + 4 < 0 and x - 2 > 0} or {x + 4 > 0 ,,and x - 2 < 0} ,,
{x < -4 and x > 2} or {x > -4 and x < 2},,
Discard x < -4 and x > 2 because it has no solutions, leaving just
x > -4 and x < 2 ,,
-4 < x < 2
