- #1
Kernul
- 211
- 7
Homework Statement
So, I'm doing a long exercise, you can check here the first part: https://www.physicsforums.com/threads/checking-if-the-following-lines-are-coplanar.885948/
The second part asks me to find, if one of the couple of lines are skew, the orthogonal line to two skew lines.
Homework Equations
The Attempt at a Solution
Here is how I did it:
I first found the directional vector of the orthogonal line, which is ##\vec v_o = \vec v_s \times \vec v_t##.
##\begin{vmatrix}
\hat i & \hat j & \hat k \\
3 & 0 & -3 \\
-12 & -4 & 8
\end{vmatrix} = (-12, 12, -12)##
After this, I'll need the parametric form of one of the two lines. In this case I'll take ##s##.
##\begin{cases}
x = 4 - \tau \\
y = 2 \\
z = \tau
\end{cases}##
Now we will need a line bundle and use the equations of the parametric form of ##s## and the vector ##\vec v_o##.
##\begin{cases}
x' = 4 - \tau - 12m\\
y' = 2 + 12m\\
z' = \tau - 12m
\end{cases}##
At this point, we will substitute the unknowns to the Cartesian form of ##t## .
##\begin{cases}
4(4 - \tau - 12m) - 2(2 + 12m) + 5(\tau - 12m) - 3 = 0 \\
2(2 + 12m) + \tau - 12m + 1 = 0
\end{cases}##
and I end up with two unique solutions for ##\tau## and ##m##.
##\begin{cases}
\tau = \frac{22}{7} \\
m = \frac{1}{42}
\end{cases}##
Now I have to substitute these in the line bundle equations so I'll have the point where the intersection between the line bundle, which is orthogonal to the line ##s## because we used the parametric form of ##s## in order to make it, and the line ##t## happens.
##\begin{cases}
x' = 4 - \frac{22}{7} - \frac{12}{42} = \frac{4}{7} \\
y' = 2 + \frac{12}{42} = \frac{16}{7} \\
z' = \frac{22}{7} - \frac{12}{42} = \frac{20}{7}
\end{cases}##
Now we know that the line we are searching for has to pass in that point and that the directional vector is ##\vec v_o##, so:
##\begin{cases}
x' = \frac{4}{7} - 12\tau\\
y' =\frac{16}{7} + 12\tau\\
z' = \frac{20}{7} - 12\tau
\end{cases}##
Is this correct? Because every time I see fractions in this kind of exercises makes me think I did something wrong.