Question 113449
{{{x^2 - 3x - 4 < 0}}}
{{{(x - 4)(x + 1) < 0}}}
OK, I've got two things multiplied together giving me less than zero
which means negative. This is like
{{{a*b < 0}}}
Here are the possibilities:
(+)*(+) = +
(-)*(-) = +
(+)*(-) = -
(-)*(+) = -
I don't want the 1st two cases, only the 2nd two.
How do I make (x + 1) negative? By making x less than -1
{{{x < -1}}}
But if {{{x < -1}}}, (x - 4) ends up being negative, too and I get
the case (-)*(-) = +, and I don't want that
So, I'll choose x so that (x - 4) is negative
{{{x < 4}}} makes it negative, but I want (x + 1) to stay positive, too
(x + 1) stays positive when {{{x > -1}}}
Now I combine these 
{{{-1 < x < 4}}}
Notice I only can use the case (-)*(+) = -
Hope you can follow this & hope I got it right, too