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# Math Question Help

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Sep 27, 2019

#1
+6180
+3

These problems don't make sense as written or I don't understand the terminology.

What row is modified to become 2R1 - R3 ?

Sep 27, 2019
#2
+684
+2

yeah that is what i was thinking

Nirvana  Sep 27, 2019
#3
+1

Rows:

-1 2      R1

0   4     R2

6    3      R3

-3   -4       R4

2R1

so,

-2  4

0    4

6    3

-3   -4

Then I suppose you want to subract 2r1-r3

so

-2-6  4-3

= -8  1

So the matrix at the end will be:

-1 2

0   4

-8  1

-3  -4

Let me know if it is wrong or correct.

Sep 27, 2019
#4
+109563
+3

Jenny (a regular poster)  explained the terminology

2R1  - R3   means that we want to multiply R1  by 2, subtract R3 from this  and put the result in R3

So....

2R1  =  -2  4

Subtracting R3  from this gives us   -8    1

So....the resulting matrix is :

-1    2

0    4

-8    1

-3   -4                     just as the Guest found  !!!!

BTW.....the more clear terminology  should be   2R1 - R3 →  R3

Sep 27, 2019
#5
+108732
+3

Hi Chris,

Why couldn't it mean .. Put the result in R1 ?

That is how I would have interpreted it.

But I am also in agreement with others that the question is incomplete.

It could mean either one.

Sep 28, 2019
#6
+109563
+2

That's the way I interpreted it, too!!

However......JennyLove  says that it means to put the result in R3

But....like you.....I find this notation very confusing   !!!!

CPhill  Sep 28, 2019
#7
+109563
+2

As an addendum to this......look at the explanation of this notation near the bottom of these answers :

https://web2.0calc.com/questions/help-on-2-matrix-questions

JennyLove  was instructed to  proceed in this manner ......

[ I still believe that this is faulty  !!!  ]

Sep 28, 2019
#8
+6180
+2

whoever is teaching this notation needs to be flogged.

whatever happened to good old elementary matrices?

Rom  Sep 29, 2019
#9
+108732
+1

I suppose they are out of fashion

When I was at school (a very long time ago)

Correct terminology and strict setting out was all important.

Now it seems children are often allowed, even encouraged, to scribble their answers on ipads etc, setting out is too diffiult on these media so it has been at least partially thrown away.

Poor notation is just an extension of this.

Young teachers cannot teach good proceedures if they were never taught them in the first place.

Melody  Sep 30, 2019
#10
+6180
+2

In this problem the elementary matrix would be

$$e=\begin{pmatrix}1&0&0&0\\0&1&0&0\\2&0&-1&0\\0&0&0&1\end{pmatrix}$$

Rom  Oct 1, 2019