Chapter 1: Vectors, Lines and Planes
Section 1.7: Planes
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Example 1.7.9
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If is the plane obtain an equation for the line that lies in P, that is perpendicular to , the line given parametrically by
and that is at a distance from M, the point of intersection of with P.
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Solution
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Mathematical Solution
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In Figure 1.7.9(a), the blue arrow represents the vector W, the direction of line L.
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Point M, the intersection of line and plane , is shown in gold.
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The red arrow denotes N, the normal to plane .
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The green arrow represents the vector that lies in plane , and is orthogonal to , the plane containing both W and N.
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The vectors , lie in the intersection of planes and , and have length 4. Their heads are 4 units from point M.
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Line will pass through the head of either of and be parallel to V.
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use plots, LinearAlgebra, Student:-VectorCalculus in
module()
local d,X,Y,Z,P,T,MM,W,N,V,U,R,H1,H2,n,v,u,uu,w,p1,p2,p3,p4,p5,p6,p7,p8,p9,p10;
d:=4:
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X:=2-3*t:
Y:=1+2*t:
Z:=3+t:
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T:=solve(eval(P,[x=X,y=Y,z=Z]),t):
MM:=eval(<X,Y,Z>,t=T):
W:=map(coeff,<X,Y,Z>,t):
N:=<coeff(P,x),coeff(P,y),coeff(P,z)>:
V:=LinearAlgebra:-CrossProduct(W,N)/2:
U:=LinearAlgebra:-CrossProduct(V,N):
R:=d*U/LinearAlgebra:-Norm(U,2):
H1:=M+R+s*V:
H2:=M-R+s*V:
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n:=RootedVector(root=MM,N):
v:=RootedVector(root=MM,V):
u:=RootedVector(root=MM,R):
uu:=RootedVector(root=MM,-R):
w:=RootedVector(root=MM,W):
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p1:=PlotVector(n,color=red,width=.2):
p2:=PlotVector(v,color=green,width=.2):
p3:=PlotVector(u,color=black,width=.2):
p4:=PlotVector(uu,color=black,width=.2):
p5:=PlotVector(w,color=blue,width=.2):
p6:=implicitplot3d(P,x=-5..5,y=1..12,z=0..10,style=surface,transparency=.9,color=red):
p7:=textplot3d({[-5.5,6,5,'W'],[2,9.5,3.5,'V'],[.3,3,2,typeset(4*`#mover(mi("U",fontstyle = "normal",fontweight = "bold"),mo("ˆ"))`)],[-.2,2.8,7.9,'N']},font=[Times,Bold,14]):
p8:=textplot3d([-11/5, 2.8, 22/5,M],font=[default,14]):
p9:=pointplot3d([-2.2,3.8,4.4],symbol=solidsphere,symbolsize=20,color=gold):
p10:=display([p1,p2,p3,p4,p5,p6,p7,p8,p9],axes=none,scaling=constrained,lightmodel=none,orientation=[90,75,85]):
print(p10);
end module:
end use:
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Figure 1.7.9(a) Normal (red), direction of (blue), direction of (green), point M (gold),vectors orthogonal to and of length 4 (black)
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Table 1.7.9(a) contains a schematic for a vector-based determination of line .
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intersects at M:.
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is direction of .
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is normal to .
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is the direction of .
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is orthogonal to V and lies in the intersection of planes P and .
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, with direction V, is at the tip of
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Table 1.7.9(a) Schematic for vector-based determination of line
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Maple Solution - Interactive
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Table 1.7.9(b) lists the steps by means of which the requisite lines can be found with the "Lines & Planes" tools in the Student MultivariateCalculus package.
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Define plane and line .
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Obtain point M as the intersection of line and plane .
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Obtain N, the normal for plane .
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Obtain W, the direction vector along line .
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Obtain , the plane containing point M and the directions N and W.
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Obtain V, the normal for plane .
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Obtain the line of intersection of planes and , then extract U, the direction of this line.
Normalize U, calling the unit vector so formed u instead of .
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Obtain m, the position vector to point M.
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Form , the vector-form of the lines in plane , 4 units from point M.
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Table 1.7.9(b) Steps for finding the requisite lines with the "Lines & Planes" tools in the Student MultivariateCalculus package
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Table 1.7.9(c) implements the calculations listed in Table 1.7.9(b).
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Tools≻Load Package: Student Multivariate Calculus
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Loading Student:-MultivariateCalculus
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Define plane
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Control-drag the equation of plane .
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Plane
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Context Panel: Assign to a Name≻
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Define line
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Make a list of the parametric equations for line .
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Line
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Context Panel: Assign to a Name≻
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Obtain point M, the intersection of line with plane
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Form a sequence of the names for the line and plane .
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Intersection
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Context Panel: Assign to a Name≻M
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Obtain the normal for plane
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Write the name of plane .
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Normal
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Context Panel: Assign to a Name≻N
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Obtain W, the direction vector along line
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Write the name of line .
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Context Panel: Evaluate and Display Inline
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Direction
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Context Panel: Assign to a Name≻W
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Obtain plane that contains point M and the directions N and W
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Write the sequence of names for point M, and vectors N and W.
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Plane
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Context Panel: Assign to a Name≻
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Obtain V, the normal for plane
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Write the name of plane .
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Context Panel: Evaluate and Display Inline
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Normal
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Context Panel: Assign to a Name≻V
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Obtain u, a unit vector in the direction of the line of intersection of planes and
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Write the sequence of names for planes and .
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Intersection
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Context Panel: Student Multivariate Calculus≻Lines & Planes≻Direction
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Context Panel: Student Multivariate Calculus≻Normalize
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Context Panel: Assign to a Name≻u
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Obtain m, the position vector to point M
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Write the name of point M.
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Context Panel: Evaluate and Display Inline
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Context Panel: Conversions≻Column Vector
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Obtain the equations of the lines that pass through the heads of and that have direction V
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Table 1.7.9(c) Implementation of the calculations listed in Table 1.7.9(b)
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Maple Solution - Coded
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Install the Student MultivariateCalculus package.
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Define plane via the Plane command.
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Define line via the Line command.
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Obtain N, the normal on plane via the GetNormal command.
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Obtain point M, the intersection of line with plane , via the GetIntersection command.
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Obtain W, the direction of line , via the GetDirection command.
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Obtain , the plane containing point M, and the directions W and N, via the Plane command.
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Obtain V, the normal on plane , via the GetNormal command.
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Obtain m, the position vector to point M.
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Obtain the equations of the lines that pass through the heads of and that have direction V
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A vector-based calculation that eschews the power of the Student MultivariateCalculus package will require a greater knowledge of Maple syntax and more human intervention, as the calculations in Table 1.7.9(d) show.
Intersect line with plane and extract the intersection point as the position vector m
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By inspection, write the vectors N and W
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Obtain and
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Obtain the two lines
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Table 1.7.9(d) Vector-based calculation of the requisite lines.
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