# Homework Help: Determining if a line is perpendicular in $R^3$

1. Feb 3, 2015

### Calpalned

1. The problem statement, all variables and given/known data
Is the line through (-2, 4, 0) and (1, 1, 1) perpendicular to the line through (2, 3, 4) and (3, -1, -8)?

2. Relevant equations
R = R0 + tV (for each line)

3. The attempt at a solution
If the lines are parallel, then the V for the two equations will be proportional to each other. How are the two V's related if they are perpendicular?

2. Feb 3, 2015

### Dick

Think dot product.

3. Feb 3, 2015

### Calpalned

I see thank you, Dick.

4. Feb 3, 2015

### Brian T

You could also use the cross product if you prefer that.

5. Feb 3, 2015

### LCKurtz

And you don't mind doing at least three times as much work...

6. Feb 3, 2015

7. Feb 3, 2015

### SammyS

Staff Emeritus
You might also want to be sure that the lines intersect and thus are not skew lines.