10

3

I define a function $f(x)$ as

```
f[x_] := x*Exp[-x] - 0.16064;
```

Then I set a variable `actualroot`

to the function `FindRoot`

, starting at $x=3$

```
actualroot = FindRoot[f[x], {x, 3}]
```

and get the output

```
{x -> 2.88976}
```

Later, I want to compare this output with a different estimate ($x\approx -2.88673$) of the root, and calculate error, so I have

```
Abs[(actualroot - estimateroot)/actualroot]
```

and I get this output:

```
Abs[(-2.88673 + (x -> 2.88976))/(x -> 2.88976)]
```

How do I get *Mathematica* to evaluate this expression? I also tried using `N[]`

function to give me a decimal evaluation, but it didn't work.

2You can use

`actualroot = FindRoot[f[x], {x, 3}][[1, 2]]`

– b.gates.you.know.what – 2012-07-13T20:27:39.393