find equation of plane through point that contains line in parametric form

3,195

Solution 1

Hint: The normal to your plane should be perpinducular to $(3,5,1)-(3,-1,0)=(1,-6,-1)$ and $(-1, 2,-3)$.

Solution 2

Well, think about this, if the plane does contain that straight line, it means

  1. ANY point from that straight line belongs to the plane too.
  2. The direction vector of the straight line is also a direction vector of the plane.

So you know that you can easily get one point and the direction vector in parametric form in a glanze: Q(4,-1,0), and $\vec{v}=(-1,2,-3)$.

So you already know a point and a direction vector.

Now, check that the other point $P(3,5,1)$ is not in the straight line. If it is inside the line, the information is redundant and incomplete. If it is not in the straight line, you can plot the vector $\vec{u}=\vec{PQ}$, and that's the 2nd direction vector you need.

So you have a point (two indeed) and 2 direction vectors. That's enough for building the plane equation.

You know you can use $(x,y,z)\cdot \left(\vec{u}\times\vec{v}\right)=0$ , and you get the equation from there.

Solution 3

Let $A(3,5,1)$, $B(4,-1,0)$ and $\vec{n}(a,b,c)$ be a normal of the plane.

Thus, $\vec{AB}(1,-6,-1)$ and $$(1,-6,-1)(a,b,c)=0$$ and $$(-1,2,-3)(a,b,c)=0$$ or $$a-6b-c=0$$ and $$-a+2b-3c=0,$$ which gives $b=-c$, $a=-5c$ and we can assume that $\vec{n}(5,1,-1)$.

Thus, we got an equation of the plane: $$5(x-3)+(y-5)-(z-1)=0$$ or $$5x+y-z-19=0.$$

Share:
3,195

Related videos on Youtube

2316354654
Author by

2316354654

Updated on September 28, 2020

Comments

  • 2316354654
    2316354654 about 3 years

    find equation of plane through point (3,5,1) and contains line x=4-t, y=2t-1, z=-3t.

    I was able to see how to do this with a parallel and perpendicular plane but I'm not sure how to apply the fact that the plane contains this line to find the plane. I have a feeling I have to use the point vertices where the x0 y0 and z0 spots are, and i'm thinking I have to do something like plug x=4-t into the x spot, or convert the line into vector form but I have a feeling that would be wrong, if I could just have a little clarification on the process that would be helpful. there's no example in the book, and the online ones are confusing, I'm hoping these plane equations will come together in my head soon because they all seem like different methods i just have to memorize.

    • rogerl
      rogerl about 6 years
      Hint: Pick two points on the line. You now have three points on the plane. Can you proceed from there?
    • 2316354654
      2316354654 about 6 years
      yes. could I simply plug in 0 for t, then 1 for t, and get points Q(4,-1,0) and then R(3,1,-3), have (3,5,1) be P, then take PQ x PR to get the coeficients, and plug P in for the p values, and simplify to get my equation?
    • 2316354654
      2316354654 about 6 years
      that leaves me with 8x +y -2z = 31
  • 2316354654
    2316354654 about 6 years
    im sorry im in a hurry and couldn't test all methods, can you tell me if my method i used in the comments above is right?
  • 2316354654
    2316354654 about 6 years
    im sorry im in a hurry and couldn't test all methods, can you tell me if my method i used in the comments above is right?
  • 2316354654
    2316354654 about 6 years
    or perhaps a better question would be how did you get (3,−1,0)=(1,−6,−1)and (−1,2,−3)
  • Michael Rozenberg
    Michael Rozenberg about 6 years
    @2316354654 Your equation of the plane is wrong because the point $(3,5,1)$ don't belong to the plane.
  • 2316354654
    2316354654 about 6 years
    then why does it say "find equation of plane through point (3,5,1) "?
  • Michael Rozenberg
    Michael Rozenberg about 6 years
    @2316354654 $8\cdot3+5-2\cdot1-31\neq0$.
  • 2316354654
    2316354654 about 6 years
    is the process at least right? maybe I made an error taking the cross product
  • Michael Rozenberg
    Michael Rozenberg about 6 years
    @2316354654 I think my answer is right. I checked it.
  • 2316354654
    2316354654 about 6 years
    oh, i thought there could be multiple answers
  • 2316354654
    2316354654 about 6 years
    how did you get 1-,2,-3?