Question Answer

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## Word to PDF converter

Does anyone know of a good Word to PDF converter? When I search for one on Google I get a lot of fishy sites coming up.

thanks

## miscellaneous questions

1. When computing the null space in matlab, are y'all getting real crazy results? I did number 10 on HW3 by hand and got it right, but when I do null(A) in octave, it returns wild decimals. Is this normal? 'null(A)' is the correct syntax, right? - Justin K

Answer: @ justin K. i am not sure if the professor has showed us a shortcut using matlab or octave to find the null space of a matrix. but i can show you a way to quick check if your answer is correct. ok so first find the null space by hand. then whatever you get multiply each one by the original matrix using matlab or octave and if you get all zeros that means your answer is correct. for example:
-> original matrix::: Let A=[ -1 -2 2; 1 2 -2; 2 4 -4]
finding the nullspace by hand you get :
-> null space solution by hand::: [-2;1;0] and [2;0;1]
lets call them
N1=[-2;1;0]
N2=[2;0;1]
so then
using matlab or octave
A*N1 it should give you [0;0;0]
A*N2 it should give you [0;0;0]
that means your solution of the nullspace by hand is correct.
sincerely Abel Barraza
hope this helped a little bit.

Excellent Question: You are right, the answers coming from the null command are MUCH different. They are related to the kind of answers we got using the rref computation. Notice that in our answers we will always have an entry that is 1. Notice that for the answers that Matlab gives there is almost never a 1; however remember we are finding a basis. In fact check that the vectors Matlab gives you are scalar multiples of the ones we found. In fact what matlab is giving are always vectors of length 1 (check that using the 'norm(v)' command).

## Homework Questions

HW 2

• # 3,4: What is meant by writing x and y as a function of z? I have the values for x, y, z, but I can't seem to remember how to resolve the (x,y) coordnates of this problem. Yeah, stupid, I know… - Justin K

ANSWER by mariacs
I had trouble with this too. It made me mad but I figured it out :)
For problem 3, I came out with:
x - 1.5y - 4.5z = -6
y + 5z = 12

I first solved for y and ended up with y = 12 - 5z. Then I solved for x:
x = -6 + 4.5z + 1.5y
x = -6 + 4.5z + 1.5(12 - 5z)
….and so on so that x = 12 - 3z.
And that's what it means by writing x and y as functions of z:
y = 12 - 5z
x = 12 - 3z
HW 6
Can someone please enlighten me on how to factor a cubic polynomial.
regards- Abel Barraza

Answer: You can have Matlab/Octave solve it for you. Type in A= [a b c d]<Enter> with a,b,c, and d being the coefficients. Then, type in roots(A)<enter>.
Example: A=[1 4 -5 21]
roots(A)
-Erik Gomez
ufffff. Awesome!! thanks man. atte: Abel Barraza
Test 3

## Gaussian Elimination Examples

page revision: 55, last edited: 22 Feb 2012 17:04
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