# Basic linear algebra help. Converting equation to matrix form

1. Sep 29, 2010

### DyslexicHobo

1. The problem statement, all variables and given/known data
Express the equation $$q=x_1 - 6x_2 + 3x_1^2 + 5x_1 x_2$$ in the matrix form $$1/2x^T Q*x+c^T x$$

2. Relevant equations
The only mention of a matrix c that I could find in my book is in the section of Gaussian elimination:

$$c= \frac {a_{ik}}{a_{kk}}$$

But I don't feel like this has anything to do with the solution form I'm trying to find.

3. The attempt at a solution
I'm not sure where to begin really. I feel like this should be a very simple problem, but I'm not sure where to start. I tried defining x = [x1 x2] and Q = [q1 q2] but I'm not sure what the "c" matrix is supposed to be.

As some background, this is taken from the review portion of my Finite Elements book.

Last edited: Sep 29, 2010
2. Sep 29, 2010

### lanedance

Q will be a 2x2 matrix, while c will be a 2x1 column vector - they have to be of that form to match the multiplication and as q is a scalar