Write the set of points greater than or equal to −5−5 but strictly less than 44, excluding 00, as a union of two intervals (if you're having trouble with this, try drawing a number line):

What we want to draw is the half closed interval:

                                          I=   [-5, 4) excluding 0,

as the union of 2 different intervals say a and b.

Let a be the interval containing the smallest value.

Then the smallest value of a is -5, and the largest possible value of a is 0, not included, if we want to write a as an interval, without "gaps", or "holes".

So a=[-5, 0)

similarly, b=(0, 4).

[-5, 4)=[-5, 0)∪(0, 4)