Math problems - help needed! :D

So, I made the topic with math problems! I have problems with Gaussian elimination method (I'm not sure if that's the right translation). Here's the photos.


http://shrani.si/f/i/13q/4Mwe2a57/dsc01351.jpg



http://shrani.si/f/36/oL/3eYmOdWz/dsc01352.jpg



http://shrani.si/f/3y/u5/1dodVqdu/dsc01353.jpg




Any ideas how to solve it? If you don't know what is it about, don't worry about it too much.

About The First Task:

Add (-3 * row1) to row2
1 -2 1 5
0 7 -4 -15
0 3 1 -1

Divide row2 by 7
1 -2 1 5
0 1 -4/7 -15/7
0 3 1 -1

Add (-3 * row2) to row3
1 -2 1 5
0 1 -4/7 -15/7
0 0 19/7 38/7

Divide row3 by 19/7
1 -2 1 5
0 1 -4/7 -15/7
0 0 1 2

Add (4/7 * row3) to row2
1 -2 1 5
0 1 0 -1
0 0 1 2

Add (-1 * row3) to row1
1 -2 0 3
0 1 0 -1
0 0 1 2

Add (2 * row2) to row1
1 0 0 1
0 1 0 -1
0 0 1 2

I Think This Is The Solution Of The Second One:


Divide row1 by 3
1 -1/3 0 1/3
-1 3 2 3
1 2 2 3

Add (1 * row1) to row2
1 -1/3 0 1/3
0 8/3 2 10/3
1 2 2 3

Add (-1 * row1) to row3
1 -1/3 0 1/3
0 8/3 2 10/3
0 7/3 2 8/3

Divide row2 by 8/3
1 -1/3 0 1/3
0 1 3/4 5/4
0 7/3 2 8/3

Add (-7/3 * row2) to row3
1 -1/3 0 1/3
0 1 3/4 5/4
0 0 1/4 -1/4

Divide row3 by 1/4
1 -1/3 0 1/3
0 1 3/4 5/4
0 0 1 -1

Add (-3/4 * row3) to row2
1 -1/3 0 1/3
0 1 0 2
0 0 1 -1

Add (1/3 * row2) to row1
1 0 0 1
0 1 0 2
0 0 1 -1

About 20a:


Add (1 * row1) to row2
1 1 -1 -4
0 2 1 -1
1 2 1 0

Add (-1 * row1) to row3
1 1 -1 -4
0 2 1 -1
0 1 2 4

Divide row2 by 2
1 1 -1 -4
0 1 1/2 -1/2
0 1 2 4

Add (-1 * row2) to row3
1 1 -1 -4
0 1 1/2 -1/2
0 0 3/2 9/2

Divide row3 by 3/2
1 1 -1 -4
0 1 1/2 -1/2
0 0 1 3

Add (-1/2 * row3) to row2
1 1 -1 -4
0 1 0 -2
0 0 1 3

Add (1 * row3) to row1
1 1 0 -1
0 1 0 -2
0 0 1 3

Add (-1 * row2) to row1
1 0 0 1
0 1 0 -2
0 0 1 3

And The Last One:



Add (-3 * row1) to row2
1 2 1 1 4
0 -4 -3 -2 -11
2 -1 -2 2 2
0 1 1 -1 1

Add (-2 * row1) to row3
1 2 1 1 4
0 -4 -3 -2 -11
0 -5 -4 0 -6
0 1 1 -1 1

Divide row2 by -4
1 2 1 1 4
0 1 3/4 1/2 11/4
0 -5 -4 0 -6
0 1 1 -1 1

Add (5 * row2) to row3
1 2 1 1 4
0 1 3/4 1/2 11/4
0 0 -1/4 5/2 31/4
0 1 1 -1 1

Add (-1 * row2) to row4
1 2 1 1 4
0 1 3/4 1/2 11/4
0 0 -1/4 5/2 31/4
0 0 1/4 -3/2 -7/4

Divide row3 by -1/4
1 2 1 1 4
0 1 3/4 1/2 11/4
0 0 1 -10 -31
0 0 1/4 -3/2 -7/4

Add (-1/4 * row3) to row4
1 2 1 1 4
0 1 3/4 1/2 11/4
0 0 1 -10 -31
0 0 0 1 6

Add (10 * row4) to row3
1 2 1 1 4
0 1 3/4 1/2 11/4
0 0 1 0 29
0 0 0 1 6

Add (-1/2 * row4) to row2
1 2 1 1 4
0 1 3/4 0 -1/4
0 0 1 0 29
0 0 0 1 6

Add (-1 * row4) to row1
1 2 1 0 -2
0 1 3/4 0 -1/4
0 0 1 0 29
0 0 0 1 6

Add (-3/4 * row3) to row2
1 2 1 0 -2
0 1 0 0 -22
0 0 1 0 29
0 0 0 1 6

Add (-1 * row3) to row1
1 2 0 0 -31
0 1 0 0 -22
0 0 1 0 29
0 0 0 1 6

Add (-2 * row2) to row1
1 0 0 0 13
0 1 0 0 -22
0 0 1 0 29
0 0 0 1 6



I Hope I Helped... even though it's too late for my help.. I think

I'll try to be faster next time!