Matrices help

[ijd5000]

Problem:

Solve for x1 , x2, x3, and x4.

The matrix is:

4 -1 0 -1 30
-1 4 -1 0 60
0 -1 4 -1 70
-1 0 -1 4 40

I keep getting fraction answers, which is a hint that its not correct (the book generally uses whole numbers).

My answers are
x1 = 425/4
x2 = 95
x3 = 255/4
x4 = 45/2

 

[daon2]

Perhaps someone here has the patience to do all of the row-reductions for you. I will just comment that using a calculator, your answers are incorrect. If you're like me, a single minus sign or a forgotten row element somewhere buried in your work caused everything to go out of wack.

As far as your images, you can use any hosting site, like tinypic.com, to upload your image. Then use the image tags

[img] ... your url ..[/img]

 

[ijd5000]

which calculator did you use, i've been trying to find a good one

 

[daon2]

I use this: http://www.bluebit.gr/matrix-calculator/linear_equations.aspx

But I highly recommend powerful software called SciLab, it's free (or Matlab if you want spend money) at http://www.scilab.org/

 

[ijd5000]

 

[daon2]

Much easier reading work than doing it

Up until step 9 is fine I think. Step 9 -> Step 10, what are you thinking?! You need to get rid of all entries in the last column above your pivot, starting with that -1/2. Then you'll have 30 for x3, which is correct.

 

[ijd5000]

I don't know what i was thinking, guess that's why they say it helps to have a fresh set of eyes lol. Thank you

 

[Bob Brown MSEE]

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