Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**mom****Member**- Registered: 2012-04-25
- Posts: 94

I have the following:

1/2 x - 4y = 5

4x + 7y = 2

I am told to multiply the first equation by -2

the transformed system is

-1x + 8y = -10

4x + 7y = 2

What is the abbreviation of the indicated operation? _R

_

Im stuck. Please help

Is it -2R

1

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

I am not sure about this mainly because I would probably have to actually have to have the text book (or sheet of paper)

that you have quoted that from to be certain. As far as I know this is not a universal concept in terms of the abbreviation.

The equation you have multiplied is done correctly - that is to say you have indeed multiplied by -2.

(As a critical observation: When you write 1/2 x it would be clearer if you wrote (1/2)x because it could be confused with (1/(2x))

which is obviously different and not what you meant. I am being picky here and you knew what you meant because the answer

you then gave was correct.)

The term "R" may mean "row". That is to say it may refer to a row operation - in this case multiplying the entire row by

a factor (in this case -2). If this is the case then I can see what you mean with your answer of -2R.

Whether this is "correct" as such needs a little more information I would think because I am not sure.

Are we defining R to be equal to the entire first row. R = [(1/2) x - 4y = 5]

If this is the case then -2R = [-x + 8y = -10]

I wonder whether you are supposed to use a subscript notation or something to indicate which row it is refering to.

With matirix calculations there is some notation to do with this. If it is solving simultaneous equations then I am not

sure what the currently taught notation is and it might vary from course to course and differ according to the country

and so on.

However it looks like a sensible answer to me.

I suppose this is designed to teach you to solve 2 simultaneous equations, or possibly 2 by 2 matrix calcuations.

To my mind at least it is the solving a problem bit, rather than what abbreviation should be used, that is the more

important thing.

*Last edited by SteveB (2013-05-20 08:05:07)*

Offline

**mom****Member**- Registered: 2012-04-25
- Posts: 94

it is row and it is subscript for the indication. i just dont know how to do that in here

thank you

Offline

**SteveB****Member**- Registered: 2013-03-07
- Posts: 535

I have looked back at the first post and I can see what you mean:

The LaTeX needed

`[math] R_1 [/math]`

You made one mistake: not using the math bits in square brackets.

around the R_1 bit as in:

If you don't use the math tags then you just get plain text !

Apart from that I agree with your answer.

*Last edited by SteveB (2013-05-20 08:32:16)*

Offline

**mom****Member**- Registered: 2012-04-25
- Posts: 94

ok thanks

Offline

Pages: **1**