# Homework Help: Constraint equations

1. Sep 27, 2010

### jhg12345

Thanks so much guys

Last edited: Sep 27, 2010
2. Sep 27, 2010

### Staff: Mentor

Let's rename b to x, since I want to use a, b, c, and d as the coordinates of this vector.
In this problem you want to find solutions for c1, c2, and c3 so that c1<1, 0, 1, 1> + c2<0, 1, 1, 2> + c3<1, 1, 1, 0> = <a, b, c, d>.

Is that enough to get you started?

3. Sep 27, 2010

### jhg12345

Yea, that's what I did and I got a matrix, but I can't get a matrix with a row of all zeros.

4. Sep 27, 2010

### Staff: Mentor

Use an augmented 4 x 4 matrix with your three vectors as the first three columns, and the coordinates a, b, c, and d as the fourth column.

From the matrix you showed, it looks like you have your three vectors as rows in a 3 x 4 matrix.

5. Sep 27, 2010

### jhg12345

ok thanks for the help so far, but Im still stuck.

Last edited: Sep 27, 2010
6. Sep 27, 2010

### Staff: Mentor

Use the third row to eliminate the 2 entry in the row above it. Then, use the 4th row to eliminate any nonzero entries above it.

Where is your 4th column? You need that to get your constraint equation.

7. Sep 27, 2010

### jhg12345

Yea, I know. Thanks for the help.