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Elementary row operations question

  • Thread starter TonyC
  • Start date
  • #1
86
0
I am working with the following equation:
|1 -2 3|
|6 -11 15|
|4 -14 21|
a. add -4 time Row1 to Row 3
b. add -6 times Row 1 to Row 2
c. add 6 times Row 2 to Row 3
d. multiply row 3 by -1/9

I have come up with the following answer:
|24 -48 72|
|180 -354 522|
|-19.99 39.99 -58.99|

Where did I go wrong?
 

Answers and Replies

  • #2
86
0
Incidently, this is a multiple choice question and my answer isn't anywhere near any of the answers to choose from.
 
  • #3
Fermat
Homework Helper
872
1
After the 1st 2 operations, you should have ended up with,

Code:
1 -2 3
0 1 -3
0 -6 9
 
  • #4
86
0
When you say first two operations, do you mean a and b or a?

What am I messing up?

After I ran a, I had:

-4 8 -12
6 -11 15
0 -6 9
 
  • #5
VietDao29
Homework Helper
1,423
2
Why are you multiplying the first row by -4???
It says add -4 times Row 1 to Row 3.
Viet Dao,
 
  • #6
86
0
What does that mean?
Do I add -4 to Row 3 or do I multiply -4 by Row 1 than add Row 1 to Row 3?
 
  • #7
VietDao29
Homework Helper
1,423
2
Add -4 times Row 1 To Row 3 means that you change Row 3 by adding -4 times Row 1 to it, and you don't change anything in Row 1, (ie: you just change Row 3).
Row 1 is: |1 -2 3|
-4 times Row 1 is : |-4 8 -12| (*)
You will add the (*) to row 3, which is:
|4 + (-4)xxxxxx-14 + 8xxxxxx21 + (-21)| = |0 -6 9|
You still keep Row 1. You only change Row 3. ie:
|1 -2 3|
|6 -11 15|
|0 -6 9|
Do the same for b, c, and d.
Viet Dao,
 
  • #8
86
0
OH, I SEE!

I have come up with:
1 -2 3
0 1 -3
0 0 1

THANK YOU!
 
  • #9
86
0
:rofl: The light bulb has come on
 

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