1. Simple Linearization Problem

I must be losing my mind because I've been over and over this one and can't see what I am doing wrong:

Find the linearization L(x) of the function $f(x) = cos(x)$ at $a = \frac{3\pi}{2}$

Here is what I have done:

$f'(x) = -sin(x)$
$f'(\frac{3\pi}{2}) = -(-1) = 1$

$L(x) = f(x) + f'(x)(x-a)$
$L(x) = cos(\frac{3\pi}{2}) + 1(x - \frac{3\pi}{2})$
$L(x) = 0 + x - \frac{3\pi}{2}$
$L(x) = x - \frac{3\pi}{2}$

And that's my answer. But when I plug it into the web site, it gets kicked back as incorrect. Can anybody see my mistake? I can't!

Thanks.

2. first line should be L(x) = f(a) + f'(a)(x-a) ... other than that, looks fine to me. I do not attempt to understand the inner workings of online answering systems.

3. Originally Posted by skeeter
first line should be L(x) = f(a) + f'(a)(x-a) ... other than that, looks fine to me. I do not attempt to understand the inner workings of online answering systems.
Personally, I hate those things!