posted by Joey .
This is a question that deals specifically with WebWork.
Here is the question:
Write the set of points from -2 to 4 but excluding -1 and 4 as a union of intervals
my solution to this would be: [-2,4]U(-1,4)
The first set includes -2 and goes up to and includes 4, the second includes everything greater than -1 and goes to everything less than 4. This way, the integer -2 is still included. BUT, this is wrong.
If you had all the points, you'd have [-2,4]
But, you have to exclude 4, leaving [-2,4)
Now, inside this interval, you exclude -1, so you have to break it up into two intervals:
Write the set of points from -5 to 1 but excluding -4 and 1 as a union of intervals