## anonymous 3 years ago Are matrices A and B inverses? Look in comments to see matrices.

1. anonymous

|dw:1375487302704:dw|

2. anonymous

just multiply them ,if your gona get identity matrix then yes they are inverse else no

3. anonymous

$A*A^{-1}=I$

4. anonymous

What do you mean by "identity matrix"

5. anonymous

identical?

6. jdoe0001

$$\bf I = \left[ \begin{matrix} 1&0\\ 0&1 \end{matrix}\right]$$

7. anonymous

And for 2x2 matrices only: $A = \left[\begin{matrix}a & b \\ c & d\end{matrix}\right]$ $A^{-1} = \frac{ 1 }{ detA } \left[\begin{matrix}d & -b \\ -c & a\end{matrix}\right]$

8. anonymous

|dw:1375487630099:dw|

9. anonymous

therefore it is not an inverse since its not all the same?

10. anonymous

|dw:1375487648610:dw|

11. jdoe0001

$$A \times B = \left[ \begin{matrix} 1&0\\ 0&1 \end{matrix}\right] = \textit{I} \implies B = A^{-1}; A = B^{-1}$$

12. anonymous

watch out with that cross symbol ^_^

13. jdoe0001

lol

14. jdoe0001

$$A \cdot B$$ :)

15. anonymous

hehe

16. anonymous

this isnt explaining anything at all guys :L

17. anonymous

i get the equation but how do i know if it is or is not?

18. jdoe0001

well, you have just have to multiply them

19. anonymous

Multiply what? AxB as a whole? The numbers in A with each other? Im sorry im feeling pretty hopeless, i just need a more in-depth explanation please ;/

20. primeralph

Yes. Inverses.

21. anonymous

5*-7=-35 -18*2=-36 therefore the answer is no? right?

22. primeralph

I just told you they are inverses.

23. anonymous

oh, okay.

24. anonymous

thanks man

25. primeralph

You're welcome.