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Determine the value for "x" such that the points A(-1, 3, 3), B(-2, 3, -1), and C(-5,6, "x") all lie on a plane that contains the origin.?

Here's what I've done (doesn't give me the right answer):

Eq 1. -1m-2n = -5

Changes to: m=-5+2n

Eq 2. 3m+3n=6

Eq 3. 4m-n="x"

Substitution (Eq 2 and 1):

3(-5+2n)+3n=6

-15+9n=6

9n=21

n=21/9

When I replace "n" with 21/9 in Eq. 3, I don't get the same number meaning the vectors don't even lie on the plane (which goes against what the questions says).

Help please!

1 Answer

Relevance
  • ?
    Lv 7
    7 years ago
    Favorite Answer

    If A, B, C and O are all in the one plane then C = aA+bB

    (-5,6,x) = a(-1, 3, 3)+b(-2, 3, -1)

    -a-2b=-5, 3a+3b=6 and 3a-b=x

    Simultaneously solve the first two equations to get a=-1 and b=3

    Substitute them into the third equation to get x = -6

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