Question #101029
1. Find a basis for the subspace of R4 spanned by the given vectors.

(1,1,-5,-6), (2,0,2,-2), (3,-1,0,8).

2. Find a subset of the vectors that forms a basis for the space spanned by the vectors, then express each vector that is not in the basis as a linear combination of the basis vectors.

v1=(1,0,1,1), v2 = (-4,4,-1,4), v3 = (2,4,5,10), v4 = (-10,4,-7,-2)

3. Find a subset of the vectors that forms a basis for the space spanned by the vectors, then express each vector that is not in the basis as a linear combination of the basis vectors.

v1=(1,-1,5,2), v2 = (-2,3,1,0), v3 = (5,-6,14,6), v4 = (0,4,2,-3), v5 = (3,15,45,2)

4. Determine whether b is in the column space of A, and if so, express b as a linear combination of the column vectors of A.

A = 3 4 B = -1
6 -9 15
1
Expert's answer
2020-01-07T07:45:17-0500

1.As the set { v1,v2,v3v_1,v_2,v_3 } span a subspace of R4R^{4}

then, c1v1+c2v2+c3v3=0c_1v_1+c_2v_2+c_3v_3=0

c1(1,1,5,6)+c2(2,0,2,2)+c3(3,1,0,8)=0c_1(1,1,-5,-6)+c_2(2,0,2,-2)+c_3(3,-1,0,8)=0

We get following equations from above equation

c1+2c2+3c3=0c_1+2c_2+3c_3=0

c1c3=0c_1-c_3=0

5c1+2c2=0-5c_1+2c_2=0

6c12c2+8c3=0-6c_1-2c_2+8c_3=0

From the above equation we can easily conclude that c1=c2=c3=0c_1=c_2=c_3=0

So,{ v1,v2,v3v_1,v_2,v_3 } are linearly independent.

Thus, the set is the basis for the subspace of R4.

2.As the set v1,v2,v3,v4v_1,v_2,v_3,v_4 span R4.

then,c1v1+c2v2+c3v3+c4v4=0c_1v_1+c_2v_2+c_3v_3+c_4v_4=0

c1(1,0,1,1)+c2(4,4,1,4)+c3(2,4,5,10)+c4(10,4,7,2)=0c_1(1,0,1,1)+c_2(-4,4,-1,4)+c_3(2,4,5,10)+c_4(-10,4,-7,-2)=0

We get equations:

c14c2+2c310c4=0c_1 -4 c_2 +2 c_3 -10 c_4 = 0

4c2+4c3+4c4=04 c_2 +4 c_3 +4 c_4 = 0

c1c2+5c37c4=0c_1 -c_2 +5 c_3 -7 c_4 = 0

c1+4c2+10c32c4=0c_1 +4 c_2 +10 c_3 -2 c_4 = 0

Solving these equations we can easily get

c1=6c3+6c4c_1 = -6 c_3 +6 c_4

c2=c3c4c_2 = -c_3 -c_4

c3=arbitraryc_3 = arbitrary

c4=arbitraryc_4 = arbitrary

{ v1,v2v_1,v_2 } span { v3,v4v_3,v_4 }

{v1,v2v_1,v_2 } spans a subspace of R4 and vectors are linearly independent.Thus,vectors serve as the basis of a subspace of R4.

3.c1v1+c2v2+c3v3+c4v4+c5v5=0c_1v_1+c_2v_2+c_3v_3+c_4v_4+c_5v_5=0

c1(1,1,5,2)+c2(2,3,1,0)+c3(5,6,14,6)+c4(0,4,2,3)+c5(3,15,45,2)=0c_1(1,-1,5,2)+c_2(-2,3,1,0)+c_3(5,-6,14,6)+c_4(0,4,2,-3)+c_5(3,15,45,2)=0

We get the following equations from the above equation.

c12c2+5c3+3c5=0c_1 -2 c_2 +5 c_3 +3 c_5 = 0

c1+3c26c3+4c4+15c5=0- c_1 +3 c_2 -6 c_3 +4 c_4 +15 c_5 = 0

5c1+c2+14c3+2c4+45c5=05 c_1 +c_2 +14 c_3 +2 c_4 +45 c_5 = 0

2c1+6c33c4+2c5=02 c_1+6 c_3 -3 c_4 +2 c_5 = 0

Solving these equations we can get:

c1=3c37c5c_1 = -3 c_3 -7 c_5

c2=c32c5c_2 =c_3 -2 c_5

c3=arbitraryc_3 = arbitrary

c4=4c5c_4 = -4 c_5

c5=arbitraryc_5 = arbitrary

{v1,v2,v4v_1,v_2,v_4 } span {v3,v5v_3,v_5 }

{ v1,v2,v4v_1,v_2,v_4 } span a subspace of R4 and vectors are linearly independent.Thus, vectors serve as the basis of a subspace of R4.

4.A=[3469]A=\begin{bmatrix} 3 & 4 \\ 6 & -9 \end{bmatrix}

B=[115]B=\begin{bmatrix} -1 \\ 15 \end{bmatrix}

B=c1(36)+c2(49)B=c_1\begin{pmatrix} 3 \\ 6 \end{pmatrix}+c_2\begin{pmatrix} 4 \\ -9 \end{pmatrix}


3c1+4c2=13c_1+4c_2=-1

6c19c2=156c_1-9c_2=15

c1=1,c2=1c_1=1,c_2=-1

Yes, B is in the column space of A as it can be expressed as a linear combination of column vectors of A.










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