Math Is Fun Forum

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Matrix proof

Not a particularly difficult question, but I don't know where I'm going wrong.

Here's what I've done:

And now I can't see how to get to the result in i)?

But this is clearly not equal to A (unless detA = 1, which my solution to part i) would suggest, but this doesn't seem right).

Where have I gone wrong? Thanks.

Last edited by Daniel123 (2008-10-10 23:36:36)

mathsyperson

Moderator

Registered: 2005-06-22

Posts: 4,900

Re: Matrix proof

The last line in (i) should be:

For (ii), I'm guessing you've taken det(A^-1) = 1, when it should actually be 1/detA.
Carry that change through and you should get back to A fairly easily.

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Why did the vector cross the road?
It wanted to be normal.

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: Matrix proof

Ahh I'm an idiot.

Thanks.