## Anita505 2 years ago Find the inverse of the following matrix A, if possible. Check that... WILL GIVE A MEDAL :)

1. inkyvoyd

The question is, will you give your calculator a medal if you did the same thing? ;)

2. inkyvoyd

If you own a graphing calculator, chances are you will be able to use it to do this math problem. I'm assuming that this is NOT homework OR testwork. If it is, I'll try to work you through the problem.

3. Anita505

|dw:1363038798101:dw|

4. Anita505

sorry we are not suppose to use a graphing calculator actually.

5. Anita505

@SithsAndGiggles

6. inkyvoyd

In this case, you might have to give us the matrix A in order to start...

7. Anita505

how?

8. Anita505

can u show me the steps on finding this solution? please i dont understand what i did wrong

9. inkyvoyd

Well, you might want to type the A matrix because I can't find the inverse of the matrix without the matrix itself xD

|dw:1363039261135:dw|

11. inkyvoyd

Also, please tell me the name of the unit/course you are taking at the moment. There are a number of ways to find the inverse of a matrix. I'm assuming you are using determinants or Gauss-Jordan elimination, but if you are using something else please let me know.

12. Anita505

section 4.5 The Gauss Jordan method for calculating Inverses.

13. inkyvoyd

Okay. Please tell me what matrix A is. I mean, the four numbers...

lol, @Anita505 can u draw ur matrix according in ur book :)

15. Anita505

oh yes haha sorry about that. :p

16. Anita505

|dw:1363039743929:dw|

17. inkyvoyd

Begin with your matrix and the identity matrix. Now, you want to make the left hand side the identity matrix, and the right hand side will be the inverse. Use elementary row operations. 6 5|1 0 2 7|0 1 Let's multiply the second row by 3, so that first number is also 6 6 5 |1 0 6 21|0 3 Now subtract the first row from the second row REMEMBER: We want the left hand side to be the identity matrix! 6 5 |1 0 0 16|-1 3 The zero in the bottom left is a start - we want to keep going. What do you think we should do next?

18. Anita505

we want to get a 1

19. Anita505

on the bottom left corner

20. Anita505

oops right**

21. inkyvoyd

Yes. so we simply divide the that bottom row by 16. 6 5 |1 0 0 1|-1/16 3/16 Next we'll find the top row by subtracting 5 times the second row 6 0|21/16 -15/16 0 1|-1/16 3/16 finally divide row one by 6. I'ma check my work to see if I got it correct xD - tell me what you got xD

22. Anita505

@inkyvoyd can you please draw out the matrix solution? this is very confusing.. to understand ahah

23. inkyvoyd

I'm afraid I can't do that - what I will do is tell you if what you get agrees with what I get. Is that fair?

24. Anita505

okay so what did u get for the first row and first column, first row and second column, and what did u get for the second row first column and second row second column

25. Anita505

|dw:1363062987282:dw|

26. inkyvoyd

Can you tell me what you got, so I can check your answer? :)

27. Anita505

my answer is incorrect tho thats why i asked u to show me what u did :p

28. inkyvoyd

29. Anita505

1 I -3 0 I 1

30. inkyvoyd

6 0|21/16 -15/16 0 1|-1/16 3/16 this is where I left off. This is only one step left - use a single easy elementary operation to make the left hand the identity matrix. and the right hand will be your answer :)

31. Anita505

so -15 I 16 3 I 16 is what u got?

32. inkyvoyd

No... the correct matrix is 7/32 -5/32 -1/16 3/16

33. Anita505

ohh okay they are in fractions oh okay thank you!

34. inkyvoyd
35. Anita505

thank you can u help me with a few more questions?