1. Nov 28, 2009

1. The problem statement, all variables and given/known data

In R^3, what does the pair of equations y=3 and z=5 represent? In other words, describe the set of points (x,y,z) such that y=3 and z=5.

3. The attempt at a solution

I drew out the individual planes y=3 and z=5. i am not sure how to describe the set of all points that satisfy both constraints?

I have to have the set of all points such that for ALL x-->y=3 and z=5.

Is that a surface? Or a line? I am thinking it has to be a line?

thoughts?

2. Nov 28, 2009

### xeno_gear

It might help to be a little more specific about the planes..

y = 3 is a plane, and it is parallel to the xz-plane.
z = 5 is a plane, and it is parallel to the xy-plane.

So the set of all (x,y,z) such that y=3 and z=5 is given by the intersection of these two planes, and since one is parallel to the xz-plane and the other is parallel to the xy-plane, then the intersection of y=3 and z=5 is a ______

3. Nov 28, 2009

line!

Though, I am not sure why it is so important to note that each line is parallel to a coordinate plane? The intersection of 'any' 2 planes is a line, correct? No matter what their orientation is?

Thanks!

4. Nov 28, 2009

### xeno_gear

well.. it's been a while since i've thought about things like that, but yeah, you're right. unless it's a trivial case where the two equations represent the same plane. either way, noting they're parallel to coordinate planes might help you visualize it better, but if you drew a picture anyway, it sounds like you're all set.

5. Nov 28, 2009