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Will Math HL accept Cramer's Rule to solve a problem?

Hey, there are a bunch of questions on linear systems of equations where you have to find a variable that makes the system have infinite solutions/no solutions/one solution.

Usually, I use Cramer's rule instead of Row reduction to solve these quickly without silly mistakes. This used to be accepted in the markschemes from a few years ago.

Now, they don't mention it. Would it still be OK to use it?
Reply 1
Avatar for arra
arra
7
I'm not familiar with the terminology of the various methods, and I'm pretty sure I don't do row reduction or whatever unless I'm trying to find a general solution.

Can you not just find the determinant and set that equal to 0? When the variable is in both the system and the equation (i.e. 2kx + 3y + z = 3k being the first row) I divide throughout by the variable to ensure that the 3 (or however many) equivalences, or whatever you call it, is an actual number, then I just find the determinant and set that to 0.

I've always received full marks. What exactly is Cramer's Method?
Reply 2
Avatar for Sybaritic
Sybaritic
OP
Original post by arra
I'm not familiar with the terminology of the various methods, and I'm pretty sure I don't do row reduction or whatever unless I'm trying to find a general solution.

Can you not just find the determinant and set that equal to 0? When the variable is in both the system and the equation (i.e. 2kx + 3y + z = 3k being the first row) I divide throughout by the variable to ensure that the 3 (or however many) equivalences, or whatever you call it, is an actual number, then I just find the determinant and set that to 0.

I've always received full marks. What exactly is Cramer's Method?


Yep, that's Cramer's method lol.

So if you've been getting full marks, that method should be acceptable. Its puzzling why they've stopped using that method in the markschemes. When did you do your Math exam?
Reply 3
Avatar for arra
arra
7
Well, the last time I remember doing this was for my Mock (I'm sitting the real one tomorrow) and it was a system of equations with whatever you said. November 2011 paper 1, I believe.

My teacher has always given me full marks, and she grades very strictly by the MS, but I haven't taken a look recently.

To be safe, after using the determinant why don't you just say because the determinant is 0 the inverse can't exist and hence no unique solution exists blah blah blah?
Reply 4
Avatar for arra
arra
7
In similar vein, I always use synthetic division for function problem involving finding algebraic factors etc. But I always see remainder theorem on the MS..

Any suggestions?

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