# Math Help - Absolute Max / Absolute Min Question

1. ## Absolute Max / Absolute Min Question

Find the absolute extrema:

$f(x) = sin x- cos x ; [0, \pi]$

Okay. So first I found the derivative of $f(x)$

$
f ' (x) = cos x + sin x$

Then, to find the critical points I must set this to zero.

$cos x + sin x = 0$

But I'm a little confused. If they were multiplying, I would do: either cos x = 0 or sin x = 0, right ? But since they're being added, I'm not really sure how to get x = ? so I can continue with the question.

2. ## help for the exercise

Hello,
sen x + cos x = 0
sen x = - cos x
(sen x/cos x) = -1
tg x = -1

In the interval [0, pi], we have:

tag x = tag(3.pi/4)

x = 3.pi/4

I hope you understand.
Bye!