# Col(a), row(a)

#### Petrus

##### Well-known member
Hello,

in exercise 11, I get b is not and w is, but the answer key says b is and w is not...? I don't understand...have I misunderstood or is the answer key wrong?

Regrds,
$$\displaystyle |\pi\rangle$$

#### Evgeny.Makarov

##### Well-known member
MHB Math Scholar
I don't know who/what facit is, but he/she/it is correct. Perhaps if you post your solution, we can discuss it.

#### MarkFL

Staff member
Petrus, I suggest if you are going to upload images that you use some sort of image editing software to rotate the image so that it is the right side up for ease of reading.

#### ZaidAlyafey

##### Well-known member
MHB Math Helper
I don't know who/what facit is, but he/she/it is correct. Perhaps if you post your solution, we can discuss it.
Somehow he is referring by facit to the textbook.

#### Petrus

##### Well-known member
Petrus, I suggest if you are going to upload images that you use some sort of image editing software to rotate the image so that it is the right side up for ease of reading.
What do you mean by rotate? The picture seem nice to me

#### MarkFL

Staff member
Yes, the facit refers to the answer key (I have edited the post), and I have rotated, cropped, re-sized and uploaded the new image.

edit: Petrus, on my computer, the image needed to be rotated clockwise 90 degrees.

#### Petrus

##### Well-known member
I don't know who/what facit is, but he/she/it is correct. Perhaps if you post your solution, we can discuss it.

after row reduce we got 1 0 -1|3
----------------------------0 1 2|-1
that means we got infinity soloution, if we set $$\displaystyle x_3=t$$ we got $$\displaystyle x_2=-1-2t$$ and $$\displaystyle x_1= 3+t$$ it indeed got soloution so it is in col(A)
Right?

Regards,
$$\displaystyle |\pi\rangle$$

- - - Updated - - -

Yes, the facit refers to the answer key (I have edited the post), and I have rotated, cropped, re-sized and uploaded the new image.

edit: Petrus, on my computer, the image needed to be rotated clockwise 90 degrees.
Strange and thanks for doing that! I did not know it needed to be rotated cause it showed correctly for me:S That is strange

#### Evgeny.Makarov

##### Well-known member
MHB Math Scholar
in exercise 11, I get b is not and w is, but the answer key says b is and w is not...?

after row reduce we got 1 0 -1|3
----------------------------0 1 2|-1
that means we got infinity soloution, if we set $$\displaystyle x_3=t$$ we got $$\displaystyle x_2=-1-2t$$ and $$\displaystyle x_1= 3+t$$ it indeed got soloution so it is in col(A)
Right?
Yes, but in post #1 you said that $b$ is not in $\text{col}(A)$.

#### Petrus

##### Well-known member
Yes, but in post #1 you said that $b$ is not in $\text{col}(A)$.
That'S cause I got actually wrong number in My matrice somehow.. Sorry My bad and now I correctly Solved it
Regards,
$$\displaystyle |\pi\rangle$$

Last edited:

#### Deveno

##### Well-known member
MHB Math Scholar
(3,2) = 3(1,1) + (-1)(0,1). This proves b is in col(A).

******

On the other question if a(1,0,-1) + b(1,1,1) = (a+b,b,b-a) = (-1,1,1), we must have