# Exam question t/f 2

1. Sep 13, 2012

### Mdhiggenz

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

I just remembered another question that I wasn't to sure about

1) if n1xn2 does not intersect the plan then n1xn2=0
I chose false for this one.

thoughts?

2. Relevant equations

3. The attempt at a solution

2. Sep 13, 2012

### voko

What are n1 and n2, and what is "the plan"?

3. Sep 13, 2012

### Mdhiggenz

Plane* sorry, n1, and n2 and vectors.

4. Sep 13, 2012

### voko

What plane is this? n1 x n2 is a vector, and for any given vector there are infinitely many planes it does not intersect.

5. Sep 13, 2012

### Mdhiggenz

Its a true or false question, don't know what else to tell you.

6. Sep 13, 2012

### voko

What is "the" plane in the question? Or was that really "a" plane?

7. Sep 13, 2012

### Staff: Mentor

I'm guessing that n1 and n2 are vectors in the plane, and "intersect" means that it (n1 x n2) intersects at a single point.

8. Sep 13, 2012

### Mdhiggenz

Indeed Mark.

9. Sep 13, 2012

### LCKurtz

You could tell us the complete and exact wording of the question. I have read up through post #8 and I still have no idea what this is about.

10. Sep 13, 2012

### Mdhiggenz

Honestly that is exactly how the question was worded.

11. Sep 13, 2012

### Staff: Mentor

Since you're going by what might be an imperfect memory of the problem statement, let's assume that it was as I said.

IOW, n1 and n2 are vectors in a plane. If n1 X n2 does not intersect the plane at a single point, then n1 X n2 = 0.

12. Sep 13, 2012

### Mdhiggenz

Ugggg why put true or false on a math exam....

13. Sep 13, 2012

### LCKurtz

What a poorly worded question then. Vectors don't intersect planes. Lines with the given vector as a direction vector might. It would better be stated as the contrapositive: If $\vec n_1 \times \vec n_2 \ne \vec 0$ a line with that direction vector intersects the plane in exactly one point.