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Vectors and conics
Attempts to answer problems in areas as diverse as science, technology and economics...
Attempts to answer problems in areas as diverse as science, technology and economics involve solving simultaneous linear equations. In this unit we look at some of the equations that represent points, lines and planes in mathematics. We explore concepts such as Euclidean space, vectors, dot products and conics.
By the end of this unit you should be able to:
 Section 1
 recognise the equation of a line in the plane;
 determine the point of intersection of two lines in the plane, if it exists;
 recognise the oneone correspondence between the set of points in threedimensional space and the set of ordered triples of real numbers;
 recognise the equation of a plane in three dimensions.
 Section 2
 explain what are meant by a vector, a scalar multiple of a vector, and the sum and difference of two vectors;
 represent vectors in and in terms of their components, and use components in vector arithmetic;
 use the Section Formula for the position vector of a point dividing a line segment in a given ratio;
 determine the equation of a line in or in terms of vectors.
 Section 3
 explain what is meant by the dot product of two vectors;
 use the dot product to find the angle between two vectors and the projection of one vector onto another;
 determine the equation of a plane in , given a point in the plane and the direction of a normal to the plane.
 Section 4
 explain the term conic section;
 determine the equation of a circle, given its centre and radius, and the centre and radius of a circle, given its equation;
 explain the focus–directrix definitions of the nondegenerate conics.
 Duration 20 hours
 Updated Wednesday 18th May 2011
 Intermediate level
 Posted under Mathematics and Statistics
Contents
 Current section: Introduction
 Learning outcomes
 1 Coordinate geometry: points, planes and lines
 1.1 Points, lines and distances in twodimensional Euclidean space
 1.2 Lines
 1.3 Parallel and perpendicular lines
 1.4 Intersection of two lines
 1.5 Distance between two points in the plane
 1.6 Points, planes, lines and distances in threedimensional Euclidean space
 1.7 Planes in threedimensional Euclidean space
 1.8 Intersection of two planes
 1.9 Distance between points in threedimensional Euclidean space
 1.10 Further exercises
 2 Vectors
 3 Dot product
 4 Conics
 Acknowledgements
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Vectors and conics
Introduction
This unit is an adapted extract from the course Pure mathematics (M208) [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]
The idea of vectors and conics may be new to you. In this unit we look at some of the ways that we represent points, lines and planes in mathematics.
In Section 1 we revise coordinate geometry in twodimensional Euclidean space, ^{2}, and then extend these ideas to threedimensional Euclidean space, ^{3}. We discuss the equation of a plane in ^{3}, but find that we do not have the tools to determine the equation of a plane, and leave this until Section 3.
In Section 2 we introduce the idea of a vector, and look at the algebra of vectors. Vectors give us a way of looking at points and lines, in the plane and in ^{3}, which is sometimes more useful than Cartesian coordinates, although the two are closely related.
In Section 3 we introduce the idea of the dot product of two vectors, and then use it to determine the general form of the equation of a plane in ^{3}.
In Section 4 we explain the origin of conics, as the curves of intersection of double cones and planes in ^{3}. The focus–directrix definitions of the nondegenerate conics, the ellipse, the parabola and the hyperbola, are given. We observe that conics are precisely the subsets of the plane determined by an equation of degree two.
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Publication details

Originally published: Wednesday, 18th May 2011
Copyright information
 CreativeCommons: The Open University is proud to release this free course under a Creative Commons licence. However, any thirdparty materials featured within it are used with permission and are not ours to give away. These materials are not subject to the Creative Commons licence. See terms and conditions. Full details can be found in the Acknowledgements section.
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