# Homework Help: Simple notation question

1. Sep 15, 2007

### mmathew23

I haven't done mathematics in a while and I have this question to do.

Describe the following subests of the plane:

a. R x {1,2,4}
b. ([0,1] U [2,3]) x[0,1]
c. ([0,1] U [2,3]) x ([0,1]x[2,3])

2. I'm actually unsure of the relevant equations used for this sort of problem.

3. Basically I think the first one is the lines x=1, x=2, x=4, y=1, y=2, and y=4.
But in the back of my mind I think it's either only the y or the x equations. If someone could help me visualize this properly I think this problem would be much easier. Thanks.

2. Sep 15, 2007

### cristo

Staff Emeritus
Well the first one is a set of points such that the x value is any real number, and the y value is one of {1,2,4}. So, the first value for y gives $\{(x,y):x\in\mathbb{R}, y=1\}$. Can you identify this as one of the lines you suggest? Doing so for the other values of y will give you your solution.

For the other questions, think in the same way.