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Posted by on Thursday, May 17, 2012 at 9:18am.

determine an equation for each plane

a) contains the point A(6,2,3), B(5,1,-3), and C(5,7,-2)

b) parallel to 2x + 6y + 4z = 1 and contains the point P(3,2,1)

  • Calculus - , Thursday, May 17, 2012 at 9:37am

    vector AB = (-1,-1,-6)
    vector AC = (-1,5,-5)

    a normal to these two vectors is (35, 1, -6) , I assume you know how to take a cross-product

    the plane has equation
    35x+ y - 6z = c
    plug in a point, e.g. A(6,2,3)
    210 + 2 - 18 = c
    c =194

    plane equation: 35x + y - 6z = 194
    check by subbing in points B and C, (they work)

    b) Since they are parallel, they must differ only in the constant
    so new equation: 2x + 6y + 4z = c
    plug in your point to find c

  • Calculus - , Thursday, May 17, 2012 at 9:38am

    (a)
    1. Find vectors AB and AC.
    2. Calculate the cross product of ABxAC, which gives the normal vector to the required plane.
    3. Form the equation of the plane. The components of the normal vector correspond to the coefficients of x, y and z of the equation of the plane.
    4. Find the constant term of the plane by passing the plane through one of the three points, i.e. substitute (xa,ya,za) into the equation and find the constant term.
    5. Optionally, check that the other points pass through the equation of the plane.


    (b)
    Parallel to 2x + 6y + 4z = 1 means that the normal is <2,6,4>.
    Take the left-hand side of the equation and evaluate with the point P(3,2,1), i.e. pass a plane parallel to 2x + 6y + 4z = 1 through the given point:
    2(3)+6(2)+4(1)=6+12+4=16
    So the required equation of the plane is
    2x + 6y + 4z = 16

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