Equations of Planes from Symmetric Equation of a Line

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SUMMARY

The discussion focuses on deriving the equations of planes from the symmetric equation of a line represented by the vector equation \(x=10t\), \(y=10t\), and \(z=10t\). The symmetric equation can be split into two separate equations: \(\frac{x-0}{10}=\frac{y-0}{10}\) and \(\frac{y-0}{10}=\frac{z-0}{10}\). By cross-multiplying these equations, the resulting plane equations are \(x - y + 0z = 0\) and \(0x + y - z = 0\). This method allows for the identification of two planes that intersect along the original line.

PREREQUISITES
  • Understanding of vector equations and symmetric equations of lines
  • Knowledge of parametric equations in three-dimensional space
  • Familiarity with the concept of planes in geometry
  • Ability to perform algebraic manipulations such as cross-multiplication
NEXT STEPS
  • Study the derivation of plane equations from parametric equations
  • Learn about the geometric interpretation of line and plane intersections
  • Explore the use of cross products to find intersections of planes
  • Investigate applications of symmetric equations in three-dimensional geometry
USEFUL FOR

Students and professionals in mathematics, particularly those studying geometry, linear algebra, or vector calculus, will benefit from this discussion. It is also useful for educators teaching concepts related to lines and planes in three-dimensional space.

Ocata
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Hello,Suppose I have a vector equation:

\begin{cases}
x=0+10t\\
y=0+10t\\
z=0+10t
\end{cases}

Which forms the symmetric equation \frac{x-0}{10}=\frac{y-0}{10}=\frac{z-0}{10}

Now, I know the symmetric equations can be split up so that you can form the two planes whose intersection yields the initial vector:

\frac{x-0}{10}=\frac{y-0}{10} and \frac{y-0}{10}=\frac{z-0}{10}

but I haven't been able to find any examples on how to get from the split symmetric equations of the line to two separate equations of a plane in standard form.

Would I just cross multiply each?

and get

Plane 1: x = y or x - y + 0z = 0
Plane 2: y = z or 0x + y - z = 0
 
Last edited:
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Yes, that is what you want. More generally, given the line with parametric equations x= At+ a, y= Bt+ b, z= Ct+ d, we can write
t= \frac{x- a}{A}= \frac{y- b}{B}= \frac{z- c}{C}

Break that into the two equations
\frac{x- a}{A}= \frac{y- b}{B}
and
\frac{y- b}{B}= \frac{z- c}{C}

Multiply the first equation by AB to get B(x- a)= A(y- b) which is the same as Bx- Ay= aB- bA.
Multiply the second equation by BC to get C(y- b)= B(z- c) which is the same as Cy- Bz= bC- cB.

Those are the equations of the two planes that intersect in the original line.
 
Thank you. Now I'm going to work in reverse on my own and see if the intersection of the two planes via cross product yields the original line.

Appreciate your clarification on this topic.
 

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