Solve Zero Matrix Problem: Find Matrix D for 2a+b-d = 3x2 Zero Matrix

[DethRose]

Ive got a homework question and i don't really understand what is being asked of me

Find a matrix D such that 2a+b-d is the 3x2 zero matrix.

i know a zero matrix is a matrix with all zeros in it so are they trying to get me to make a matrix with all zeros or what?

please help i have been staring at this question for like an hour

 

[franznietzsche]

What are a and b supposed to be? 2a+b should be the same as d if 2a+b-d = 0.

 

[DethRose]

i don't know that all I've got for a question i don't really know where to start

 

[HallsofIvy]

Then the only answer you can give is "d= 2a+ b"!

 

[DethRose]

the answer in the back of the book is

0 6
5 14
-9 9

 

[shmoe]

Find a matrix D such that 2a+b-d is the 3x2 zero matrix.

On it's own, this doesn't make any sense. What are a, b, and d? Are a and b 3x2 matrices you were given earlier? Is little "d" the same as big "D"? There has to more to the question, I suggest you type it out exactly as it appears.

 

[HallsofIvy]

the answer in the back of the book is
0 6
5 14
-9 9

Then a and b must have been given! Read the problem carefully! Perhaps this problem referred to matrices a and b from another problem.

 

[DethRose]

the way i stated it at the beginning is exactly how its put in the textbook

 

[DethRose]

Find a matrix D such that 2a+b-D is the 3x2 zero matrix.

sorry didnt notice i had 2 different d's now it is the exact question

 

[shmoe]

It still makes no sense as written. Again, what are a and b? Were they defined earlier? Is this a multi-part question where a and b were defined in an earlier part? An earlier problem? An example in the text? They have to come from somewhere, or this question and answer is total nonsense.

 

[DethRose]

i just phoned my prof and he said he forgot to put this on the board:

A= 1 3
2 5
-1 2

B= -2 0
1 4
-7 5

 

[shmoe]

Aha!

No problems anymore then?

 

[DethRose]

ive been working on it and I am not really sure how to go about doing it?

 

[shmoe]

You now have A and B. You want to find a matrix D where 2A+B-D is the zero matrix. Write D in terms of A and B (Halls did this for you above) and do the arithmetic.