A plane is a flat surface which is two-dimensional
Imagine a flat piece of paper that continues on forever in both directions
A plane in often denoted using the capital Greek letter?Π
The vector form of the equation of a plane can be found using?two direction vectors?on the plane
The direction vectors must be
parallel?to the plane
not parallel?to each other
therefore they will?intersect?at some point on the plane
The formula for finding the?vector equation?of a plane is
Where?r?is the?position vector?of any point on the plane
a?is the?position vector?of a known point on the plane
b?and?c?are two?non-parallel direction?(displacement)?vectors?parallel to the plane
λ and μ are scalars
The formula is?given in the formula booklet?but you must make sure you know what each part means
As?a?could be the position vector of?any?point on the plane and?b?and?c?could be?any non-parallel?direction vectors on the plane there are infinite vector equations for a single plane
How do I determine whether a point lies on a plane?
Solve two of the equations first to find the values of λ and μ that satisfy the first two equation and then check that this value also satisfies the third equation
If the values of λ and μ do not satisfy all three equations, then the point?r?does not lie on the plane
Exam Tip
Worked Example
(b)? ? ? ? Determine whether the point D with coordinates (-2, -3, 5) lies on the plane.
Equation of a Plane in Cartesian Form
How do I find the vector equation of a plane in cartesian form?
The?cartesian?equation of a plane is given in the form
How do I find the equation of a plane in Cartesian form given the vector form?
The?Cartesian?equation of a plane can be found if you know
the?normal vector?and
a?point?on the plane
The?vector equation of a plane?can be used to find the?normal vector?by finding the?vector product?of the two direction vectors
A vector product is always perpendicular to the two vectors from which it was calculated
The vector?a?given in the vector equation of a plane is a?known point?on the plane
Once you have found the normal vector then the point?a?can be used in the formula?n???r?=?a???n?to find the equation in Cartesian form
Exam Tip
In an exam, using whichever form of the equation of the plane to write down a normal vector to the plane is always a good starting point
Worked Example
a)? ? ? ?Find the equation of the plane in its Cartesian form.