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Chapter 9-Vectors Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors INSERT FIGURE 9-1-1 Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Vectors Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Vector Algebra DEFINTION: The sum v+w of two vectors v=<v1,v2> and w=<w1,w2> is formed by adding the vectors componentwise: Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Vector Algebra EXAMPLE: Add the vectors v = <−3, 9> and w = <1, 8>. DEFINITION: The zero vector 0 is the vector both of whose components are 0. DEFINITION: If v = <v1, v2> is a vector and l is a real number then we define the scalar multiplication of v by l to be Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors The Length (or Magnitude) of a Vector THEOREM: If v is a vector and l is a scalar, then Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Unit Vectors and Directions Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Unit Vectors and Directions DEFINITION: Let v and w be nonzero vectors. We say that v and w have the same direction if dir(v) =dir(w). We say that v and w are opposite in direction if dir(v) = −dir(w). We say that v and w are parallel if either (i) v and w have the same direction or (ii) v and w are opposite in direction. Although the zero vector 0 does not have a direction, it is conventional to say that 0 is parallel to every vector. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Unit Vectors and Directions THEOREM: Vectors v and w are parallel if and only if at least one of the following two equations holds: (i) v = 0 or (ii) w = lv for some scalar l. Moreover, if v and w are both nonzero and w = l v, then v and w have the same direction if 0 < l and opposite directions if l < 0. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Unit Vectors and Directions EXAMPLE: For what value of a are the vectors <a,−1> and <3, 4> parallel? Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors An Application to Physics EXAMPLE: Two workers are each pulling on a rope attached to a dead tree stump. One pulls in the northerly direction with a force of 100 pounds and the other in the easterly direction with a force of 75 pounds. Compute the resultant force that is applied to the tree stump. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors The Special Unit Vectors i and j i=<1,0> and j=<0,1> Suppose that v=<3,-5> and w=<2,4>. Express v, w, and v+w in terms of i and j. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors The Triangle Inequality EXAMPLE: Verify the Triangle Inequality for the vectors v = <−3, 4> and w = <8, 6>. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.1 Vectors in the Plane Chapter 9-Vectors Quick Quiz Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in ThreeDimensional Space Chapter 9-Vectors EXAMPLE: Sketch the points (3,2,5), (2,3,-3), and (-1,-2,1). Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Distance THEOREM: The distance d(P,Q) between points P=(p1, p2, p3) and Q=(q1, q2, q3) is given by Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Distance EXAMPLE: Determine what set of points is described by the equation Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Distance DEFINITION: Let P0 = (x0, y0, z0) be a point in space and let r be a positive number. The set is the set of all points inside the sphere This set is called the open ball with center P0 and radius r. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Vectors in Space Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Vector Operations EXAMPLE: Suppose v=<3,0,1> and w=<0,4,2>. Calculate v+w, and sketch the three vectors. EXAMPLE: Suppose v=<2,-1,1>. Calculate 3v and -4v. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors The Length of a Vector If v=<v1,v2,v3> is a vector, then the length or magnitude of v is defined to be Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Unit Vectors and Directions EXAMPLE: Is there a value of r for which u=<-1/3,2/3,r> is a unit vector? EXAMPLE: Suppose that v=<4,3,1> and w=<2,b,c>. Are there values of b and c for which v and w are parallel? Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.2 Vectors in Three-Dimensional Space Chapter 9-Vectors Quick Quiz Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors The Algebraic Definition of the Dot Product DEFINITION: The dot product vw of two vectors v and w is the sum of the products of corresponding entries of v and w. EXAMPLE: Let u = <2, 3,−1>, v = <4, 6,−2>, and w = <−2,−1,−7>. Calculate the dot products u · v, u · w, and v · w. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors The Algebraic Definition of the Dot Product THEOREM: Suppose that u, v, and w are vectors and that l is a scalar. The dot product satisfies the following elementary properties: Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors The Algebraic Definition of the Dot Product EXAMPLE: Let u=<3,2> and v=<4,-5>. Calculate (u v)u+(v u)v Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors A Geometric Formula for the Dot Product THEOREM: Let v and w be nonzero vectors. Then the angle q between v and w satisfies the equation Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors A Geometric Formula for the Dot Product EXAMPLE: Calculate the angle between the two vectors v=<2,2,4>and w=<2,-1,1>. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors A Geometric Formula for the Dot Product Cauchy-Schwarz Inequality: EXAMPLE: Verify that the two vectors v = <2, 2, 4> and w = <12, 13, 24> satisfy the Cauchy-Schwarz Inequality. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors A Geometric Formula for the Dot Product DEFINTION: Let q be the angle between nonzero vectors v and w. If q = p/2 then we say that the vectors v and w are orthogonal or mutually perpendicular. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors A Geometric Formula for the Dot Product THEOREM: Let v and w be any vectors. Then: a) v and w are orthogonal if and only if v · w = 0. b) v and w are parallel if and only if c) If v and w are nonzero, and if q is the angle between them, then v and w are parallel if and only if q = 0 or q = p. In this case, v and w have the same direction if q = 0 and opposite directions if q = p. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors A Geometric Formula for the Dot Product EXAMPLE: Consider the vectors u = <2, 3,−1>, v = <4, 6,−2>, and w = <−2,−1,−7>. Are any of these vectors orthogonal? Parallel? Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors Projection THEOREM: If v and w are nonzero vectors then the projection Pw(v) of v onto w is given by The length of Pw(v) is given by Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors Projection EXAMPLE: Let v = <2, 1,−1> and w = <1,−2, 2>. Calculate the projection of v onto w, the projection of w onto v, and calculate the lengths of these projections. Also calculate the component of v in the direction of w and the component of w in the direction of v. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors Projection and the Standard Basis Vectors EXAMPLE: Let v = <2,-6,12>. Calculate Pi(v), Pj(v), and Pk(v) and express v as a linear combination of these projections. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors Direction Cosines and Direction Angles EXAMPLE: Calculate the direction cosines and direction angels for the vector Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors Applications EXAMPLE: A tow truck pulls a disabled vehicle a total of 20,000 feet. In order to keep the vehicle in motion, the truck must apply a constant force of 3, 000 pounds. The hitch is set up so that the force is exerted at an angle of 30 with the horizontal. How much work is performed? Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.3 The Dot Product and Applications Chapter 9-Vectors Quick Quiz 1. Calculate <1, 2,−1> · <3, 4, 2>. 2. Use the arccosine to express the angle between <6, 3, 2> and <4,−7, 4>. 3. For what value of a are <1, a,−1> and <3, 4, a> perpendicular? 4. Calculate the projection of <3, 1,−1> onto <8, 4, 1>. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Cross Product of Two Spatial Vectors DEFINTION: If v = <v1, v2, v3> and w = <w1,w2,w3>, then we define their cross product v × w to be Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Cross Product of Two Spatial Vectors THEOREM: If v and w are vectors, then v × w is orthogonal to both v and w. EXAMPLE: Let v = <2,−1, 3> and w = <5, 4,−6>. Calculate v × w. Verify that v × w is orthogonal to both v and w. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Relationship between Cross Products and Determinants If v = <v1, v2, v3> and w = <w1,w2,w3>, then EXAMPLE: Use a determinant to calculate the cross product of v = <2,−1, 6> and w = <−3, 4, 1>. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors Algebraic Properties of the Cross Product If u, v, and w are vectors and l and m are scalars, then Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors Algebraic Properties of the Cross Product THEOREM: If v is any vector, then v×v = 0. More generally, if u and v are parallel vectors then u×v = 0. EXAMPLE: Give an example to show that the cross product does not satisfy a cancellation property. Give an example to show that the cross product does not satisfy the associative property. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors A Geometric Understanding of the Cross Product EXAMPLE: Find the standard unit normal for the pairs (i, j) and (j, k) and (k, i). Find also the standard unit normal for the pairs (j, i) and (k, j) and (i, k). Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors A Geometric Understanding of the Cross Product THEOREM: Let v and w be vectors. Then a) b) If v and w are nonzero, then where q [0,p] denotes the angle between v and w; c) v and w are parallel if and only if v × w = 0; d) If v and w are not parallel, then v × w points in the direction of the standard unit normal for the pair (v,w). Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors A Geometric Understanding of the Cross Product EXAMPLE: Let v = <1,−3, 2> and w = <1,−1, 4>. What is the standard unit normal vector for (v,w)? Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors Cross Products and the Calculation of Area THEOREM: Suppose that v and w are nonparallel vectors. The area of the triangle determined by v and w is The area of the parallelogram determined by v and w is EXAMPLE: Find the area of the parallelogram determined by the vectors v=<-2,1,3> and w=<1,0,4>. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Triple Scalar Product DEFINITION: If u, v, and w are given vectors, then we define their triple scalar product to be the number (u×v) · w. EXAMPLE: Calculate the triple scalar product of u = <2,−1, 4>, v = <7, 2, 3>, and w = <−1, 1, 2> in two different ways. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Triple Scalar Product THEOREM: The triple scalar product of u = <u1, u2, u3>, v = <v1, v2, v3>, and w = <w1,w2,w3> is given by the formula Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Triple Scalar Product EXAMPLE: Use the determinant to calculate the volume of the parallelepiped determined by the vectors <−3, 2, 5>, <1, 0, 3>, and <3,−1,−2>. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors The Triple Scalar Product THEOREM: Three vectors u ,v, and w are coplanar if and only if u · (v × w) = 0. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors Triple Vector Products DEFINITION: If u, v, and w are given spatial vectors, then each of the vectors u × (v × w) and (u × v) × w is said to be a triple vector product of u, v, and w. EXAMPLE: Let v and w be perpendicular spatial vectors. Show that and Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.4 The Cross Product and Triple Product Chapter 9-Vectors Quick Quiz 1. Calculate <2, 1, 2> × <1,−2,−1>. 2. Find the area of the parallelogram determined by <2, 1,−2> and <1, 1, 0>. 3. Find the standard unit normal vector for the ordered pair (<2, 1,−2>, <1, 1, 0>) . 4. True or false: a) v × w = w × v b) u × (v × w) = (u × v) × w c) u · v × w = u × v · w? Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Cartesian Equations of Planes in Space THEOREM: Let V be a plane in space. Suppose that n=<A,B,C> is a normal vector for V and that P0=(x0,y0,z0) is a point on V. Then is a Cartesian equation for V. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Cartesian Equations of Planes in Space THEOREM: Suppose at least one of the coefficients A, B, C is nonzero. Then the solution set of the equation A(x−x0)+B(y−y0)+C(z−z0) = 0 is the plane that has <A,B,C> as a normal vector and passes through the point (x0, y0, z0). The solution set of the equation Ax + By + Cz = D is a plane that has <A,B,C> as a normal vector. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Cartesian Equations of Planes in Space EXAMPLE: Find an equation for the plane V passing through the points P = (2,−1, 4), Q = (3, 1, 2), and R = (6, 0, 5). EXAMPLE: Find the angle between the plane with Cartesian equation x − y − z = 7 and the plane with Cartesian equation −x + y − 3z = 6. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Parametric Equations of Planes in Space THEOREM: If P0 = (x0, y0, z0) is a point on a plane V and if u = <u1, u2, u3> and v = <v1, v2, v3> are any two nonparallel vectors that are perpendicular to a normal vector for V, then V consists precisely of those points (x, y, z) with coordinates that satisfy the vector equation When written coordinatewise, equation above yields parametric equations for V: Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Parametric Equations of Planes in Space EXAMPLE: Find parametric equations for the plane V whose Cartesian equation is 3x − y + 2z = 7. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Parametric Equations of Lines in Space THEOREM: The line in space that passes through the point P0 = (x0, y0, z0) and is parallel to the vector m = <a, b, c> has equation Here P = (x, y, z) is a variable point on the line. In coordinates the equation may be written as three parametric equations: Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Parametric Equations of Lines in Space Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Cartesian Equations of Line in Space Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Cartesian Equations of Line in Space EXAMPLE: Find parametric equations of the line of intersection of the two planes x − 2y + z = 4 and 2x + y − z = 3. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Cartesian Equations of Line in Space EXAMPLE: Find parametric equations of the line of intersection of the two planes x − 2y + z = 4 and 2x + y − z = 3. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Calculating Distance THEOREM: Suppose that P = (x0, y0, z0) is a point and that V is a plane. Let n = <A,B,C> be a normal vector for V and let Q = (x1, y1, z1) be any point on V. The distance between P and V is equal to Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Calculating Distance EXAMPLE: Find the distance between the point P = (3,−8, 3) and the plane V whose Cartesian equation is 2x + y − 2z = 10. Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved 9.5 Lines and Planes in Space Chapter 9-Vectors Quick Quiz Calculus, 2ed, by Blank & Krantz, Copyright 2011 by John Wiley & Sons, Inc, All Rights Reserved