Are you saying that you do not know what the union symbol
means?
The fact that x= -3 and x= 1 make the two sides
equal tells you that the inequality is one way or the other through out the three intervals,
,
, and
. Plato told you that the solution
cannot be (1, 3) because x= 0 is in that interval and 0 does not satisfy the inequality. You really should, then, check one point in each of the other intervals. x= 2 is in the interval
.
so x= 2 and, so, every number in
satisfies it. x= -4 is in
and
so x= -4 and, therefore, every number in
satisifes the inequality.
That is, any number in
or in
will satisfy the inequality. A point is in
if and only if it is in A
or in B, by definition.