Question 993270
<pre>
Draw D and E on number lines

D:

<===============&#9675;------------------------------
-3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11 12

E:

-------------------------------&#9679;==============>
-3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11 12

D &#8745; E = ?

That asks for the set of numbers which the two graphs
have in common.  They have NO elements in common, so
the interval notation is () or the empty set &#8960;. 

D &#8746; E = ?

That asks for the set of numbers which are part of
either or both sets.  So we put the two graphs together
on the same number line and get

<===============&#9675;--------------&#9679;==============>
-3 -2 -1  0  1  2  3  4  5  6  7  8  9 10 11 12

The interval notation is

{{{matrix(1,5,"(",-infinity,",",2,")")}}}{{{"U"}}}{{{matrix(1,5,"[",7,",",infinity,")")}}}

Edwin</pre>