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Elementary matrix question

When I multiply out my elementary matrices, it doesn't equal the inverse. What have I done wrong?

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Original post by cooldudeman
,,,


E4 is incorrect. In particular the -3 should be in a_12, not a_13.
Original post by ghostwalker
E4 is incorrect. In particular the -3 should be in a_12, not a_13.


Thanks no wonder. I know matrix multiplication is not associative but if I jumbled the order of the elementary matrices, would it still equal the inverse?
Original post by cooldudeman
Thanks no wonder. I know matrix multiplication is not associative
Matrix multiplication IS associative. It is not commutative however.

but if I jumbled the order of the elementary matrices, would it still equal the inverse?
Not in general, no.
Original post by cooldudeman
Thanks no wonder. I know matrix multiplication is not associative but if I jumbled the order of the elementary matrices, would it still equal the inverse?


Matrix multiplication IS associative. It's not commutative, in general.
Original post by DFranklin
Matrix multiplication IS associative. It is not commutative however.

Not in general, no.


Original post by ghostwalker
Matrix multiplication IS associative. It's not commutative, in general.


Thanks, always get mixed up with the two.

Also could you check if I did this correctly please, 4d.

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Original post by cooldudeman
Thanks, always get mixed up with the two.

Also could you check if I did this correctly please, 4d.


The first two look fine.

Your third one is the equation of a plane, not a line.
Original post by ghostwalker
The first two look fine.

Your third one is the equation of a plane, not a line.


How would I get the 'standard' equation?

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Original post by cooldudeman
How would I get the 'standard' equation?

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Eliminate the parameter from the parametric one.

See here
Original post by ghostwalker
Eliminate the parameter from the parametric one.

See here


So 3-x=y-1=1/3 +z/3?

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Original post by cooldudeman
So 3-x=y-1=1/3 +z/3?

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Yes.

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