6.3 Vectors in the Plane Ref. p. 424

6.3 Vectors in the Plane Many quantities in geometry and physics, such as area, time, and temperature, can be represented by a single real number. Other quantities, such as force and velocity, involve both magnitude and direction and cannot be completely characterized by a single real number. To represent such a quantity, we use a directed line segment. The directed line segment PQ has initial point P and terminal point Q and we denote its magnitude (length) by . Q Terminal Point P PQ Initial Point

Vector Representation by Directed Line Segments Let u be represented by the directed line segment from P = (0,0) to Q = (3,2), and let v be represented by the directed line segment from R = (1,2) to S = (4,4). Show that u = v. Using the distance formula, show that u and v have the same length. Show that their slopes are equal. S 4 v 3 R Q 2 u 1 Slopes of u and v are both P 1 2 3 4

Component Form of a Vector The component form of the vector with initial point P = (p1, p2) and terminal point Q = (q1, q2) is PQ The magnitude (or length) of v is given by

Find the component form and length of the vector v that has initial point (4,-7) and terminal point (-1,5) 6 Let P = (4, -7) = (p1, p2) and Q = (-1, 5) = (q1, q2). 4 Then, the components of v = are given by 2 v1 = q1 – p1 = -1 – 4 = -5 -2 2 4 -2 v2 = q2 – p2 = 5 – (-7) = 12 -4 Thus, v = -6 and the length of v is -8

Vector Operations The two basic operations are scalar multiplication and vector addition. Geometrically, the product of a vector v and a scalar k is the vector that is times as long as v. If k is positive, then kv has the same direction as v, and if k is negative, then kv has the opposite direction of v. v ½ v 2v -v

Definition of Vector Addition & Scalar Multiplication Let u = and v = be vectors and let k be a scalar (real number). Then the sum of u and v is u + v = and scalar multiplication of k times u is the vector

Vector Operations Ex. Let v = and w = . Find the following vectors. a. 2v b. w – v 10 4 8 2v 6 3 w 4 2 -v v 2 1 -4 -2 2 -2 1 2 3 4 5 -1 w - v

Writing a Linear Combination of Unit Vectors Let u be the vector with initial point (2, -5) and terminal point (-1, 3). Write u as a linear combination of the standard unit vectors of i and j. 6 Solution 10 4 (-1, 3) 8 2 6 -2 u 2 4 8j -2 4 -4 2 (2, -5) -3i Graphically, it looks like… -6 -4 -2 2 -8 -2

Writing a Linear Combination of Unit Vectors Let u be the vector with initial point (2, -5) and terminal point (-1, 3).Write u as a linear combination of the standard unit vectors i and j. Begin by writing the component form of the vector u.

Unit Vectors u = unit vector Find a unit vector in the direction of v =

Vector Operations Let u = -3i + 8j and let v = 2i - j. Find 2u - 3v. 2u - 3v = 2(-3i + 8j) - 3(2i - j) = -6i + 16j - 6i + 3j = -12i + 19 j

6.3 Homework Page 433 Every other odd 3 – 59 and 67, 71, 73 & 79 3, 7, 11, 15, 19, 23, 27, 31, 35, 39, 43, 47, 51, 55, 59, 67, 71, 79.