# Homework Help: Evaluating matrices

1. Apr 27, 2006

### lakitu

hi there how would you go about evaluating a matrices? for example. evaluate A

A=

(-3)
(11)
(6)

i need to know this for my homework? it sounds simple but my book does not cover this. Any help would be great.

Kind Regards

Lakitu

2. Apr 27, 2006

### J77

`Evaluate' in what way?

And is...

$$A=\left(\begin{array}{c} -3 & 11 & 6 \end{array}\right)$$

3. Apr 27, 2006

### HallsofIvy

You don't "evaluate" a matrix, just as you don't evaluate a number! You can, of course, evaluate a matrix function just as you can evaluate a numerical function.

If
$$f(x)= \left(\begin{array}{c} -3x \ x^2 & 4x^3 \ 6x \end{array}\right)$$
Then it would make sense to evaluate that matrix (function) at, say, x= 2.

4. Apr 27, 2006

### lakitu

i see, what about Evaluate | u | does that make sense?

5. Apr 27, 2006

### HallsofIvy

For a given value of u, yes. It makes sense to "evaluate" any formula in one or more variables for given values of those variables. "Evaluate" means to determine the value of a formula when replacing the variables by numbers.

6. Apr 27, 2006

### robphy

Is your "u" a square matrix? If so, then "Evaluate |u|" might mean "Compute the determinant of the square matrix u". In the context of HallsofIvy's post, the "formula" is the rule to compute the determinant of a square matrix and the "variable" is the square matrix u.

7. Apr 28, 2006

### J77

Yeah - that makes sense.

For $$u=(-3, 11, 6)$$

The magnitude $$|u|=\sqrt{(-3)^2+11^2+6^2}$$