Quiz Solutions for MATH 304 - Vector Operations, Quizzes of Linear Algebra

The solutions to quiz 2 of math 304, focusing on vector operations. Topics covered include finding the length of vectors, determining if one vector is shorter than another, finding unit vectors, projections, and orthogonal vectors.

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Pre 2010

Uploaded on 08/19/2009

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MATH 304 Quiz 2 Solutions
February 6, 2007 Name
Put your answers in the space provided. Show your reasoning. Calculators may not be used. The maximum
score on this quiz is 6 points.
1. 4 points Consider the following two vectors in R3:u= [āˆ’2,1,3]Tand v= [3,3,4]T.
1a. Prove that uis shorter than v.
||u||2= 4 + 1 + 9 = 14,||v||2= 9 + 9 + 16 = 34. Therefore uis shorter than v
1b. Compute the distance from uto v
The distance from uto vis ||vāˆ’u|| =p(3 āˆ’(āˆ’2))2+ (3 āˆ’1)2+ (4 āˆ’3)2=√25+4+1=√30
1c. Find an unit vector in the direction opposite to u
From 1a. the length of uis √14. The answer is āˆ’1
√14 [āˆ’2,1,3]T
1d. Find the projection of uonto v.
The projection is uĀ·v
vĀ·vv=āˆ’6+3+12
9+9+16 v=9
34 [3,3,4]T
1e. Find a non-zero vector which is orthogonal to u
Two possible answers are [āˆ’1,1,āˆ’1]Tor [0,3,āˆ’1]T
1f. Find uvT
uvT=


āˆ’2
1
3


[3,3,4] = 


āˆ’6āˆ’6āˆ’8
334
9 9 12



2. 2 points Let Wbe the subspace of R4spanned by u1= [1,1,0,0]Tand u2= [1,āˆ’1,0,0]T. Find a basis
for W⊄. Circle your answer.
There are many answers. One is














0
0
1
1





,





0
0
1
2















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MATH 304

Quiz 2 Solutions February 6, 2007 Name

Put your answers in the space provided. Show your reasoning. Calculators may not be used. The maximum score on this quiz is 6 points.

  1. 4 points Consider the following two vectors in R^3 : u = [āˆ’ 2 , 1 , 3]T^ and v = [3, 3 , 4]T^.

1a. Prove that u is shorter than v.

||u||^2 = 4 + 1 + 9 = 14, ||v||^2 = 9 + 9 + 16 = 34. Therefore u is shorter than v

1b. Compute the distance from u to v

The distance from u to v is ||vāˆ’u|| =

√ (3 āˆ’ (āˆ’2))^2 + (3 āˆ’ 1)^2 + (4 āˆ’ 3)^2 =

1c. Find an unit vector in the direction opposite to u

From 1a. the length of u is

  1. The answer is

[āˆ’ 2 , 1 , 3]T

1d. Find the projection of u onto v.

The projection is

u Ā· v v Ā· v

v =

v =

[3, 3 , 4]T

1e. Find a non-zero vector which is orthogonal to u

Two possible answers are [āˆ’ 1 , 1 , āˆ’1]T^ or [0, 3 , āˆ’1]T

1f. Find uvT

uvT^ =

  

   [3,^3 ,^ 4] =

  

  

  1. 2 points Let W be the subspace of R^4 spanned by u 1 = [1, 1 , 0 , 0]T^ and u 2 = [1, āˆ’ 1 , 0 , 0]T^. Find a basis

for W ⊄. Circle your answer.

There are many answers. One is

    

   

   

   

   

    