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An airplane flies due north at an airspeed of 550 mph. The wind is blowing from the northwest at 50 mph. What is the ground speed of the airplane?

Approximately 516 mph

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Key concepts

  • Vectors are used to represent quantities that have both magnitude and direction.
  • We can add vectors by using the parallelogram method or the triangle method to find the sum. We can multiply a vector by a scalar to change its length or give it the opposite direction.
  • Subtraction of vectors is defined in terms of adding the negative of the vector.
  • A vector is written in component form as v = x , y .
  • The magnitude of a vector is a scalar: v = x 2 + y 2 .
  • A unit vector u has magnitude 1 and can be found by dividing a vector by its magnitude: u = 1 v v . The standard unit vectors are i = 1 , 0 and j = 0 , 1 . A vector v = x , y can be expressed in terms of the standard unit vectors as v = x i + y j .
  • Vectors are often used in physics and engineering to represent forces and velocities, among other quantities.

For the following exercises, consider points P ( −1 , 3 ) , Q ( 1 , 5 ) , and R ( −3 , 7 ) . Determine the requested vectors and express each of them a. in component form and b. by using the standard unit vectors.

P Q

a. P Q = 2 , 2 ; b. P Q = 2 i + 2 j

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Q P

a. Q P = −2 , −2 ; b. Q P = −2 i 2 j

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P Q + P R

a. P Q + P R = 0 , 6 ; b. P Q + P R = 6 j

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2 P Q 2 P R

a. 2 P Q 2 P R = 8 , −4 ; b. 2 P Q 2 P R = 8 i 4 j

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The unit vector in the direction of P Q

a. 1 2 , 1 2 ; b. 1 2 i + 1 2 j

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The unit vector in the direction of P R

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A vector v has initial point ( −1 , −3 ) and terminal point ( 2 , 1 ) . Find the unit vector in the direction of v . Express the answer in component form.

3 5 , 4 5

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A vector v has initial point ( −2 , 5 ) and terminal point ( 3 , −1 ) . Find the unit vector in the direction of v . Express the answer in component form.

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The vector v has initial point P ( 1 , 0 ) and terminal point Q that is on the y -axis and above the initial point. Find the coordinates of terminal point Q such that the magnitude of the vector v is 5 .

Q ( 0 , 2 )

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The vector v has initial point P ( 1 , 1 ) and terminal point Q that is on the x -axis and left of the initial point. Find the coordinates of terminal point Q such that the magnitude of the vector v is 10 .

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For the following exercises, use the given vectors a and b .

  1. Determine the vector sum a + b and express it in both the component form and by using the standard unit vectors.
  2. Find the vector difference a b and express it in both the component form and by using the standard unit vectors.
  3. Verify that the vectors a , b , and a + b , and, respectively, a , b , and a b satisfy the triangle inequality.
  4. Determine the vectors 2 a , b , and 2 a b . Express the vectors in both the component form and by using standard unit vectors.

a = 2 i + j , b = i + 3 j

a. a + b = 3 i + 4 j , a + b = 3 , 4 ; b. a b = i 2 j , a b = 1 , −2 ; c. Answers will vary; d. 2 a = 4 i + 2 j , 2 a = 4 , 2 , b = i 3 j , b = −1 , −3 , 2 a b = 3 i j , 2 a b = 3 , −1

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a = 2 i , b = −2 i + 2 j

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Let a be a standard-position vector with terminal point ( −2 , −4 ) . Let b be a vector with initial point ( 1 , 2 ) and terminal point ( −1 , 4 ) . Find the magnitude of vector −3 a + b 4 i + j .

15

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Let a be a standard-position vector with terminal point at ( 2 , 5 ) . Let b be a vector with initial point ( −1 , 3 ) and terminal point ( 1 , 0 ) . Find the magnitude of vector a 3 b + 14 i 14 j .

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Source:  OpenStax, Calculus volume 3. OpenStax CNX. Feb 05, 2016 Download for free at http://legacy.cnx.org/content/col11966/1.2
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