# Lines and planes relationship

### Points, Lines, Planes and Their Relationships | Geometric Definitions and Axioms | Uzinggo

All figures in Geometry are made of points, lines, and planes; however, these terms are undefined. Example 3: Draw and label a figure for each relationship. The three possible plane-line relationships in three dimensions. (Shown in each case is only a portion of the plane, which extends infinitely far.) In analytic geometry, the intersection of a line and a plane in three-dimensional space can be. Practice the relationship between points, lines, and planes. For example, given the drawing of a plane and points within 3D space, determine whether the points .

In software, one would test if where division by would cause overflow, and uses this as the robust condition for n1 and n2 to be parallel in practice. When not parallel, is a direction vector for the intersection line L since u is perpendicular to both n1 and n2, and thus is parallel to both planes as shown in the following diagram.

That is, we need to find a point that lies in both planes. We can do this by finding a common solution of the implicit equations for P1 and P2.

But there are only two equations in the 3 unknowns since the point P0 can lie anywhere on the 1-dimensional line L. So we need another constraint to solve for a specific P0. There are a number of ways this could be done: A Direct Linear Equation. This is will be true when the z-coordinate uz of is nonzero. So, one must first select a nonzero coordinate of u, and then set the corresponding coordinate of P0 to 0.

Further, one should choose the coordinate with the largest absolute value, as this will give the most robust computations. Suppose thatthen lies on L. Solving the two equations: The denominator here is equal to the non-zero 3rd coordinate of u. B Line Intersect Point. If one knows a specific line in one plane for example, two points in the planeand this line intersects the other plane, then its point of intersection, I, will lie in both planes.

Thus, it is on the line of intersection for the two planes, and the parametric equation of L is: One way of constructing a line in one plane that must intersect the other plane is to project one plane's normal vector onto the other plane. This gives a line that must always be orthogonal to the line of the planes' intersection.

So, the projection of n2 on P1 defines a line that intersects P2 in the sought for point P0 on L.

Then the projected line in P1 is L1: C 3 Plane Intersect Point. This always works since: Why is the c not solved for? Remember that there are an infinite number of equations for the line, each of which is multiple of the other.

This method always works for any distinct P and Q. There is of course a formula for a, b, c also. This can be found expressed by determinants, or the cross product.

Find the equations of these lines.

Note the special cases. Line through 3, 4 and 1, Line through 3, 4 and -6, Line through 3, 4 and 3, 7. Here is this computation.

### Incidence Relations in the Plane and in Space

By definition, two parallel lines in a Euclidean plane never meet. The study of plane geometry can be extended, however, to allow for the possibility of two parallel lines eventually meeting at infinity. A two dimensional plane that allows such a possibility is called a projective plane. Although we are not concerned here with a study of the projective plane, it is interesting to note that the idea of parallel lines meeting at infinity is believed to have originated during the Renaissance, when artists were developing techniques for adding perspective to their drawings basically to take account of the kind of visual effect that makes it appear that railway tracks converge at some perceived "vanishing point".

**Calculus 3 Lecture 11.5: Lines and Planes in 3-D**

Parallel lines converge at a common "vanishing point" Incidence relations in three-dimensional space A three dimensional space also contains points and lines. Unlike a two-dimensional space such as our Euclidean planea three-dimensional space can also contain many planes. In fact, a plane in a three-dimensional space is analogous to a line in a two-dimensional space in the sense that two planes are either parallel with one another or intersect one another. On the other hand, lines may be non-parallel but not intersect one another, and both lines and points can be coincident with many different intersecting planes simultaneously.

### Line–plane intersection - Wikipedia

As you have probably realised, there are a significantly greater number of possibilities when it comes to incidence relations in three-dimensional space. There are, however, some basic axioms that can be assumed for three-dimensional space: Line l is the only line that passes through both points. In two-dimensions, a line must lie totally within the plane in order to exist. This means that all the points that make up the line also lie completely within the plane.

It also means that for any line that passes through two points in a plane, the line must also lie completely within the plane.

The relationship between lines and planes in a three-dimensional space is obviously going to be more complex. There are in fact three possibilities pertaining to lines in a three-dimensional space: By definition, any pair of axes will intersect one another at right angles, and there will be a single plane that contains both axes.

The plane containing both the x and y axes is depicted in the figure as a grid. Line l is incident with the plane at a single point. The y axis is also incident with the plane, and with each of the other two axes, at a single point. It is also perpendicular to the plane and both of the other two axes. We can thus see two examples of lines that lie within a plane the x and y axes and two examples of lines that intersect the plane at a single point the z axis and line l.

The diagram below shows the same plane as before. Line l passes through both points, and is parallel with the plane by virtue of the fact that the z coordinates for both points are the same. Line l does not intersect the plane that contains the x and y axes What else can we say about lines and planes in a three-dimensional space?

We can say that if two lines intersect, they are incident at precisely one point.

That is true in both two and three dimensions. We can also say that there exists one plane, and only one plane, that contains both lines. If two lines do not intersect, there are two possibilities: There will however be many lines that are contained by the plane that are parallel with line l.

## Line-Plane Intersection

In the illustration below, points A and B have the same coordinates as previously. Line m passes through points C and D and lies completely within the plane containing the x and y axes. Note points C and D have the same x and y coordinates as points A and B respectively.