solve the following inequation: x-5/x+2 is smaller than zero.
Answers
Explanation:
(x+5)/(x+2)<0
A very stodgy mechanical way of looking at this is to say that the expression will be negative if either (x+5) < 0 or (x+2) < 0, but not both
so we look at these pairs
PAIR A
(x+5) < 0 and (x+2) > 0
this requires x < -5 and x > -2, so no solution
PAIR B
(x+5) > 0 and (x+2) < 0
this requires x > -5 and x < -2, so this solution works
further refining this approach, if x = 5, then the numerator is zero, not <0. so we must exclude x = 5
if x = -2, we have a singularity
3/(0^-) = - oo
so the complete answer appears to be
x in (-5, -2]
the obvious temptation here must to be to cross multiply ie to say that
if
(x+5)/(x+2)<0
then
(x+5)/(x+2) * (x+2) < 0 * (x+2)
\implies x+5 <0, qquad x < -5
but that doesn't work with inequalities. worth thinking about.