Point on the plain?
Similar to checking whether a specific point lies on a line you can also check whether the point lies on the plane.
Method
- Insert the position vector of the point (P/V) or its coordinates (C).
- Solve equation (V/C) or system of equations (P)
- Check if solvable
P - Parametric equation
V - Vector equation of a plane
C - Cartesian equation
Remember
Example (parametric form)
$P(2|1|1)$,
$\text{E: } \vec{x} = \begin{pmatrix} 3 \\ 0 \\ 0 \end{pmatrix} + r \cdot \begin{pmatrix} 1 \\ 1 \\ 0 \end{pmatrix}$ $+ s \cdot \begin{pmatrix} 1 \\ 5 \\ 2 \end{pmatrix}$
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Insert $P$
The position vector (vector with the coordinates of the point) of $P$ is used for $\vec{x}$ in $E$.$\begin{pmatrix} 2 \\ 1 \\ 1 \end{pmatrix}$ $=\begin{pmatrix} 3 \\ 0 \\ 0 \end{pmatrix} + r \cdot \begin{pmatrix} 1 \\ 1 \\ 0 \end{pmatrix}$ $+ s \cdot \begin{pmatrix} 1 \\ 5 \\ 2 \end{pmatrix}$
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Set up system of equations
Now we set up an equation system and solve it. Every line is an equation.- $2=3+r+s$
- $1=r+5s$
- $1=2s$
From III. you get $s=\frac12$, which is used in II..
$1=r+5\cdot\frac12\quad|-\frac52$
$r=-\frac32$ -
Test with I.
$r$ and $s$ are used for the sample in the unused equation (here: I.).$2=3+r+s$
Since there is no contradiction and it is a true statement, the point lies on the plane.
$2=3-\frac32+\frac12$
$2=2$
Example (Vector form)
$P(2|1|-1)$,
$\text{E: } \left(\vec{x} - \begin{pmatrix} 2 \\ 1 \\ 1 \end{pmatrix}\right) \cdot \begin{pmatrix} 2 \\ -2 \\ 4 \end{pmatrix}=0$
-
Insert $P$
The position vector (vector with the coordinates of the point) of $P$ is used for $\vec{x}$ in $E$.$\left(\begin{pmatrix} 2 \\ 1 \\ -1 \end{pmatrix} - \begin{pmatrix} 2 \\ 1 \\ 1 \end{pmatrix}\right) \cdot \begin{pmatrix} 2 \\ -2 \\ 4 \end{pmatrix}$ $=0$
-
Solve equation
The equation can be simplified first.$\begin{pmatrix} 2-2 \\ 1-1 \\ -1-1 \end{pmatrix} \cdot \begin{pmatrix} 2 \\ -2 \\ 4 \end{pmatrix}=0$
$\begin{pmatrix} 0 \\ 0 \\ -2 \end{pmatrix} \cdot \begin{pmatrix} 2 \\ -2 \\ 4 \end{pmatrix}=0$
Now apply the scalar product on the left side of the equation.
$0\cdot2+0\cdot(-2)+(-2)\cdot4$ $=0$
$-8\neq0$
=> Contradiction, point is not on the plane
Example (cartesian form)
$P(2|1|1)$,
$\text{E: } 2x-2y+4z=6$
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Insert coordinates of $P$
The individual coordinates of $P$ are used for x, y and z.$2\cdot2-2\cdot1+4\cdot1=6$
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Solve equation
The equation can be solved very easily.$2\cdot2-2\cdot1+4\cdot1=6$
$6=6$=> true statement, the point lies on the plane