# TI-89 Integrating Incorrectly

• September 28th 2008, 01:00 AM
RedBarchetta
TI-89 Integrating Incorrectly
This is what my calculator is giving me:

$
\int {\cos (1 - x)dx = \sin (x - 1)}
$

This is obviously wrong. Could anyone explain why it's doing this?
• September 28th 2008, 01:06 AM
Moo
Hello,
Quote:

Originally Posted by RedBarchetta
This is what my calculator is giving me:

$
\int {\cos (1 - x)dx = \sin (x - 1)}
$

This is obviously wrong. Could anyone explain why it's doing this?

I'm finding it correct :)

It's just that -sin(x)=sin(-x) and hence the result ;)
• September 28th 2008, 01:08 AM
Chop Suey
It is not wrong.

$\int \cos{(1-x)} dx = -\sin{(1-x)} = \sin{(-(1-x))} = \sin{(x-1)}$

Recall that Sine is an odd function:
$\sin{(-u)} = -\sin{u}$
• September 28th 2008, 02:24 AM
RedBarchetta
I didn't notice the change from (1-x) to (x-1) (Rofl)