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Vectors in space · Vectors

Equation of a plane in space

A line needs a point and one direction vector. A plane, being a two-dimensional surface within space, needs a point and two directions (or, equivalently, a single vector perpendicular to all of them: the normal vector). This gives rise to several ways of writing its equation, all equivalent.

Before you start, make sure you know: Scalar product (1st Bachillerato)
Before you start, make sure you know: Equations of a line in the plane (1st Bachillerato)

Vector and parametric equations

Perspective drawing of a plane determined by a point A and two non-parallel direction vectors u and v. A u v
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Determine the equation of the plane $\pi$ containing the line $r$ given by: $$r \equiv \begin{cases} x = 1 + 2\lambda \\ y = -1 + \lambda \\ z = 3\lambda \end{cases}$$…

Determine the equation of the plane $\pi$ containing the line $r$ given by:

$$r \equiv \begin{cases} x = 1 + 2\lambda \\ y = -1 + \lambda \\ z = 3\lambda \end{cases}$$

and parallel to line $s$, which passes through points $P(0, 2, 1)$ and $Q(1, 2, 4)$. Justify why the direction vector of $s$ cannot be proportional to that of $r$ in order for the plane to be uniquely determined.

Solve
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Find the value of the parameter $k \in \mathbb{R}$ so that the points $A(1, 0, 1)$, $B(0, 2, 1)$, $C(2, 1, 0)$ and $D(k, k, 2)$ are coplanar. Once $k$ is found, write…

Find the value of the parameter $k \in \mathbb{R}$ so that the points $A(1, 0, 1)$, $B(0, 2, 1)$, $C(2, 1, 0)$ and $D(k, k, 2)$ are coplanar. Once $k$ is found, write the equation of the plane containing them in parametric form.

Solve

General equation: point and normal vector

Perspective drawing of a plane with a point P, a normal vector orthogonal to the surface and a vector contained in it joining P to a general point X. P n = (A, B, C)

A common case: if a line $r$ has direction vector $\vec v$, the plane perpendicular to $r$ has $\vec v$ as its normal vector.

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An engineer is designing the base of a component using CAD software. The base must be a plane passing through point $P(2, -1, 3)$ with a normal vector…

An engineer is designing the base of a component using CAD software. The base must be a plane passing through point $P(2, -1, 3)$ with a normal vector $\vec{n} = (3, 2, -4)$. Calculate the general equation of the plane that defines this base.

X Y Z π 2 −1 3 n(3, 2, −4) P(2, −1, 3)
Solve
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It is desired to install a spotlight whose beam path is perpendicular to a metal plate. If the path of the light beam is given by the line…

It is desired to install a spotlight whose beam path is perpendicular to a metal plate. If the path of the light beam is given by the line $r \equiv \frac{x-1}{2} = \frac{y+3}{-1} = \frac{z}{4}$, find the equation of the plane containing the metal plate, knowing that it passes through the point $M(0, 4, -2)$.

Solve

The plane through three points

Plane determined by three non-collinear points A, B and C forming a triangle in space. A B C
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In a virtual reality scenario, three sensors are located at points $A(1, 0, 0)$, $B(0, 2, 0)$ and $C(0, 0, 3)$. Determine the general equation of the plane containing…

In a virtual reality scenario, three sensors are located at points $A(1, 0, 0)$, $B(0, 2, 0)$ and $C(0, 0, 3)$. Determine the general equation of the plane containing these three sensors.

X Y Z O A (1, 0, 0) B (0, 2, 0) C (0, 0, 3)
Solve
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An architect is designing a flat roof for a small pavilion. The roof must rest on three pillars whose upper ends are located at the points $A(2, 0, 3)$, $B(0, 4, 3)$ and…

An architect is designing a flat roof for a small pavilion. The roof must rest on three pillars whose upper ends are located at the points $A(2, 0, 3)$, $B(0, 4, 3)$ and $C(1, 1, 5)$, where the units are in metres.

  1. a) Obtain the general or implicit equation of the plane containing the roof.
  2. b) Calculate the points of intersection of this plane with the coordinate axes to determine where the anchors would be located if the roof extended to touch the main walls (axes).
X Y Z O Roof A(2,0,3) B(0,4,3) C(1,1,5) Px(?,0,0) Py(0,?,0) Pz(0,0,?) π: ?x + ?y + ?z + ? = 0
Solve

Intercept form

Plane cutting the coordinate axes at the intercept points a, b and c according to the intercept form of the equation. (a,0,0) (0,0,c) (0,b,0)
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An architect uses the "intercept equation" to define a sloping roof that intersects the coordinate axes at points $(4, 0, 0)$, $(0, 3, 0)$ and $(0, 0, 2)$. Write its…

An architect uses the "intercept equation" to define a sloping roof that intersects the coordinate axes at points $(4, 0, 0)$, $(0, 3, 0)$ and $(0, 0, 2)$. Write its equation directly and convert it to the general form $Ax + By + Cz + D = 0$.

X Y Z O (4, 0, 0) (0, 3, 0) (0, 0, 2) a=4 b=3 c=2
Solve
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A plane $\pi$ intersects the coordinate axes at points $X(a, 0, 0)$, $Y(0, b, 0)$ and $Z(0, 0, c)$. It is known that the plane passes through the point $P(1, 2, 2)$ and…

A plane $\pi$ intersects the coordinate axes at points $X(a, 0, 0)$, $Y(0, b, 0)$ and $Z(0, 0, c)$. It is known that the plane passes through the point $P(1, 2, 2)$ and that the distances from the origin to the intersection points are equal ($a = b = c$).

  1. a) Write the general equation of the plane.
  2. b) Calculate the volume of the tetrahedron formed by the origin and the three intersection points with the axes.
X(a,0,0) Y(0,b,0) Z(0,0,c) P(1,2,2) O x y z a b c
Solve

The pencil of planes

Animation of a pencil of planes: one plane (dashed) rotates fully around the line r, which stays fixed, passing through different positions; all the planes of the pencil contain the axis r. π₁ π₂ r
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Consider the pencil of planes whose axis is the line of intersection of the planes $\pi_1 \equiv 2x - y + z - 3 = 0$ and $\pi_2 \equiv x + y - 2z + 1 = 0$. Find the…

Consider the pencil of planes whose axis is the line of intersection of the planes $\pi_1 \equiv 2x - y + z - 3 = 0$ and $\pi_2 \equiv x + y - 2z + 1 = 0$. Find the plane belonging to this pencil that passes through the midpoint of the line segment with endpoints $A(1, 2, -1)$ and $B(3, 0, 5)$.

Solve

Summary

See all the exercises in this section