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# FP1 Matrix Algebra watch

1. How would you go about the following question.

A= [2 -4] AB= 2[0 4] A-1 (inverse) = 1/8 [-2 4]
[3 -2] [1 4] [-3 2]

Find what B is

P.S. sorry for the bad notations

thanks
2. (Original post by sister_x)
How would you go about the following question.

A= [2 -4] AB= 2[0 4] A-1 (inverse) = 1/8 [-2 4]
[3 -2] [1 4] [-3 2]

Find what B is

P.S. sorry for the bad notations

thanks
multiply AB by A-1: ABA-1 which = B
3. are you sure?
I don't get the answer out.
its question 3b pg 142 of the edexcel FP1 text book, if you have it.
The answer should be [1 2]
[1/2 -1]
4. (Original post by dichr0ic)
ABA-1 = B
5. (Original post by dichr0ic)
multiply AB by A-1: ABA-1 which = B
sort of right, with matricies you must pre-multiply, so it'd be A^-1AB and pre-multiply the other side aswell
6. (Original post by blueJ-)
sort of right, with matricies you must pre-multiply, so it'd be A^-1AB and pre-multiply the other side aswell
ty

i thought what i wrote looked a bit weird
7. sorry what do you mean A^-1AB??
8. (Original post by sister_x)
sorry what do you mean A^-1AB??
A^-1 is the inverse of A so they cancel
9. so basically I do inverse A multiplied by AB which will equal B?
I tried that it doesn't work
its question 3 in the attachment
Attached Images

10. (Original post by sister_x)
so basically I do inverse A multiplied by AB which will equal B?
I tried that it doesn't work
its question 3 in the attachment
The inverse of A is not needed in part b, I think the question was a little ambigious so no one bothered trying to work it out and just said what you could try. Anyway

(2 -4) (a b) = (0 8)
(3 -2) (c d) = (2 8)

That's what the question tells you, now you've got to find a b c d which gives you matrix B.
11. thanks I managed to get the answer out LOL wasn't too hard in the end

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