TI-89 Integrating Incorrectly

**RedBarchetta** · September 28th 2008, 01:00 AM

This is what my calculator is giving me:

$<br /> \int {\cos (1 - x)dx = \sin (x - 1)} <br />$

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

**Moo** · September 28th 2008, 01:06 AM

Hello,

Originally Posted by RedBarchetta

This is what my calculator is giving me:

$<br /> \int {\cos (1 - x)dx = \sin (x - 1)} <br />$

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

**Chop Suey** · September 28th 2008, 01:08 AM

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:
$\sin{(-u)} = -\sin{u}$

**RedBarchetta** · September 28th 2008, 02:24 AM

I didn't notice the change from (1-x) to (x-1)

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