Find the equation of the plane which contains the point (3,2,-3) and the line (x,y,z)

  1. 1. The problem statement, all variables and given/known data
    Find the equation of the plane which contains the point (3,2,-3) and the line: (x,y,z) = (7,-4,5) + t (0,-2,2)



    2. Relevant equations
    Point-Normal equation?
    a(x-x0)+b(y-y0)+c(z-z0) = 0

    Not sure if this is related.


    3. The attempt at a solution

    First off:

    The line (xyz) should be (7,-4,5) + t (0,-2,2) which becomes (7, -4-2t, 5 +7t). And then yea...

    I'm behind :(. I've been sick for the past 2 weeks and I don't understand my friends' notes. So I'm not asking for any of you to solve this for me, but if someone could point me in the right direction and help me on interpreting the question, then that would be great.

    Thanks.
     
  2. jcsd
  3. Dick

    Dick 25,735
    Science Advisor
    Homework Helper

    Re: Find the equation of the plane which contains the point (3,2,-3) and the line (x,

    You can use the normal equation once you find a normal. You've got one direction vector which is parallel to the plane which is the direction vector to the line. Find another one by taking the difference between your point and any point on the line. Then use the cross product.
     
  4. HallsofIvy

    HallsofIvy 40,305
    Staff Emeritus
    Science Advisor

    Re: Find the equation of the plane which contains the point (3,2,-3) and the line (x,

    Or- just take two different values of t to find two different points on the line. You now have three points in the plane. You know how to find the plane containing three given points, don't you?
     
  5. Re: Find the equation of the plane which contains the point (3,2,-3) and the line (x,

    Do I use
    ax + by + cz + d = 0
    to get the equation of each point and solve for the system of equations?

    Is there a difference between "passing through the points" and "contains the points" in terms of planes?
     
  6. Dick

    Dick 25,735
    Science Advisor
    Homework Helper

    Re: Find the equation of the plane which contains the point (3,2,-3) and the line (x,

    If you don't know how to find the equation of a line using three points, why don't you just try to find a normal? You seemed to be ok with that.
     
  7. HallsofIvy

    HallsofIvy 40,305
    Staff Emeritus
    Science Advisor

    Re: Find the equation of the plane which contains the point (3,2,-3) and the line (x,

    That is certainly one possible way to do it. Notice that you get three equations to solve for four coefficients but that is okay: any multiple of the equation of the plane is also an equation of the plane. You can take any one of a, b, c, or d to be 1, say.

    But the way most people learn to find the plane containing three given points is to determine the vectors from one of the points to the other two and take the cross product of those- which leads back to the method Dick is suggesting.

    I don't know why but, geometrically, I tend to think of a line as "passing through" points and a plane as "containing" points! No, there is no difference at all.
     
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