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Holt McDougal Geometry
8-6 Vectors8-6 Vectors
Holt Geometry
Warm UpWarm Up
Lesson PresentationLesson Presentation
Lesson QuizLesson Quiz
Holt McDougal Geometry
Holt McDougal Geometry
8-6 Vectors
Warm UpFind AB.
1. A(0, 15), B(17, 0)
2. A(–4, 2), B(4, –2)
Solve each equation. Round to the nearest tenth or nearest degree.
3. 4.
5. 6.
6.3 3.1
38° 50°
Holt McDougal Geometry
8-6 Vectors
Find the magnitude and direction of a vector.
Use vectors and vector addition to solve real world problems.
Objectives
Holt McDougal Geometry
8-6 Vectors
vectorcomponent formmagnitudedirectionequal vectorsparallel vectorsresultant vector
Vocabulary
Holt McDougal Geometry
8-6 Vectors
The speed and direction an object moves can be represented by a vector. A vector is a quantity that has both length and direction.
You can think of a vector as a directed line segment. The vector below may be named
Holt McDougal Geometry
8-6 Vectors
A vector can also be named using component form.The component form <x, y> of a vector lists thehorizontal and vertical change from the initial point to the terminal point. The component form of is <2, 3>.
Holt McDougal Geometry
8-6 Vectors
Example 1A: Writing Vectors in Component Form
Write the vector in component form.
The horizontal change from H to G is –3 units.
The vertical change from H to G is 5 units.
So the component form of is <–3, 5>.
Holt McDougal Geometry
8-6 Vectors
Example 1B: Writing Vectors in Component Form
with M(–8, 1) and N(2, –7)
Write the vector in component form.
Subtract the coordinates of the initial point from the coordinates of the terminal point.
= <x2 – x1, y2 – y1>
= <2 – (–8), –7 – 1>
= <10, –8>
Substitute the coordinates of the given points.
Simplify.
Holt McDougal Geometry
8-6 Vectors
Check It Out! Example 1a
Write the vector in component form.
The horizontal change is –3 units.
The vertical change is –4 units.
So the component form of is <–3, –4>.
Holt McDougal Geometry
8-6 Vectors
Check It Out! Example 1b
Write each vector in component form.
the vector with initial point L(–1, 1) and terminal point M(6, 2)
Subtract the coordinates of the initial point from the coordinates of the terminal point.
Substitute the coordinates of the given points.
Simplify.
= <x2 – x1, y2 – y1>
= <6 – (–1), 2 – 1>
= <7, 1>
Holt McDougal Geometry
8-6 Vectors
When a vector is used to represent speed in a given direction, the magnitude of the vector equals the speed. For example, if a vector represents the course a kayaker paddles, the magnitude of the vector is the kayaker’s speed.
The magnitude of a vector is its length. The magnitude of a vector is written
Holt McDougal Geometry
8-6 Vectors
Example 2: Finding the Magnitude of a Vector
Draw the vector <–1, 5> on a coordinate plane. Find its magnitude to the nearest tenth.
Step 1 Draw the vector on a coordinate plane. Use the origin as the initial point. Then (–1, 5) is the terminal point.
Step 2 Find the magnitude. Use the Distance Formula.
Holt McDougal Geometry
8-6 Vectors
Check It Out! Example 2
Draw the vector <–3, 1> on a coordinate plane.Find its magnitude to the nearest tenth.
Step 1 Draw the vector on a coordinate plane. Use the origin as the initial point. Then (–3, 1) is the terminal point.
Step 2 Find the magnitude. Use the Distance Formula.
Holt McDougal Geometry
8-6 Vectors
The direction of a vector is the angle that it makes with a horizontal line. This angle is measured counterclockwise from the positive x-axis. The direction of is 60°.
The direction of a vector can also be given as a bearing relative to the compass directions north, south, east, and west. has a bearing of N 30° E.
Holt McDougal Geometry
8-6 Vectors
Example 3: Finding the Direction of a Vector
The force exerted by a skier is given by the vector <1, 4>. Draw the vector on a coordinate plane. Find the direction of the vector to the nearest degree.
Step 1 Draw the vector on a coordinate plane. Use the origin as the initial point.
So mA = tan-1(4) 76°.
Step 2 Find the direction.
Draw right triangle ABC as shown. A is the angle formed by the vector and the x-axis, and
A C
B
Holt McDougal Geometry
8-6 VectorsCheck It Out! Example 3
The force exerted by a tugboat is given by the vector <7, 3>. Draw the vector on a coordinate plane. Find the direction of the vector to the nearest degree.
Step 1 Draw the vector on a coordinate plane. Use the origin as the initial point.
A
B
CStep 2 Find the direction.
Draw right triangle ABC as shown. A is the angle formed by the vector and the x-axis, and
Holt McDougal Geometry
8-6 Vectors
Two vectors are equal vectors if they have the samemagnitude and the same direction. For example, . Equal vectors do not have to have the same initial point and terminal point.
Holt McDougal Geometry
8-6 Vectors
Two vectors are parallel vectors if they have the same direction or if they have opposite directions. They may have different magnitudes. For example, Equal vectors are always parallel vectors.
Holt McDougal Geometry
8-6 Vectors
Example 4: Identifying Equal and Parallel Vectors
Identify each of the following.
A. equal vectors
B. parallel vectors
Identify vectors with the same magnitude and direction.
Identify vectors with the same or opposite directions.
Holt McDougal Geometry
8-6 Vectors
Check It Out! Example 4
Identify each of the following.
a. equal vectors
b. parallel vectors
Identify vectors with the same magnitude and direction.
Identify vectors with the same or opposite directions.
Holt McDougal Geometry
8-6 Vectors
The resultant vector is the vector that represents the sum of two given vectors. To add two vectors geometrically, you can use the head-to-tail method or the parallelogram method.
Holt McDougal Geometry
8-6 Vectors
Holt McDougal Geometry
8-6 Vectors
To add vectors numerically, add their components. If = <x1, y1> and = <x2, y2>, then
= <x1 + x2, y1 + y2>.
Holt McDougal Geometry
8-6 Vectors
Example 5: Aviation Application
An airplane is flying at a constant speed of 400 mi/h at a bearing of N 70º E. A 60 mi/h wind is blowing due north. What are the plane’s actual speed and direction? Round the speed to the nearest tenth and the direction to the nearest degree.Step 1 Sketch vectors for the airplane and the wind.
70°400
Airplane
20°y
x
S
W E
N
60
S
W E
N Wind
Holt McDougal Geometry
8-6 Vectors
Example 5 Continued
Step 2 Write the vector for the airplane in component form. The airplane’s vector has a magnitude of 400 mi/h and makes an angle of 20º with the x-axis.
so x = 400 cos20° 375.9.
The airplane’s vector is <375.9, 136.8>.
so y = 400 sin20° 136.8.
Holt McDougal Geometry
8-6 Vectors
Step 3 Write the vector for the wind in component form. Since the wind moves 60 mi/h in the direction of the y-axis, it has a horizontal component of 0 and a vertical component of 60. So its vector is <0, 60>.
The resultant vector in component form is <375.9, 196.8>.
Step 4 Find and sketch the resultant vector . Add the components of the airplane’s vector and the wind vector.
<375.9, 136.8> + <0, 60> = <375.9, 196.8>.
Example 5 Continued
Holt McDougal Geometry
8-6 Vectors
Step 5 Find the magnitude and direction of the resultant vector. The magnitude of the resultant vector is the airplane’s actual speed (or ground speed).
The angle measure formed by the resultant vector gives the airplane’s actual direction.
Example 5 Continued
+
Holt McDougal Geometry
8-6 Vectors
Lesson Quiz: Part I
Round angles to the nearest degree and other values to the nearest tenth.
1. Write with S(–5, 2) and T(8, –4) in
component form.
2. Write with magnitude 12 and direction 36° in
component form.
3. Find the magnitude and direction of the vector
<4, 5>.
<13, –6>
<9.7, 7.1>
6.4; 51°
Holt McDougal Geometry
8-6 Vectors
Lesson Quiz: Part II
4. Find the sum of the vectors <2, –4> and <3, 6>. Then find the magnitude and direction of the resultant vector.
5. A boat is heading due east at a constant speed of 35 mi/h. There is an 8 mi/h current moving north. What is the boat’s actual speed anddirection?
<5, 2>; 5.4; 22°
35.9 mi/h; N 77° E