As explained in this videa from 15:00 when I try to derive d(cos (x)/d(x) I get sin x not - sin x

[hollow grotto]

https://www.youtube.com/watch?v=S0_qX4VJhMQ&list=PLZHQObOWTQDMsr9K-rj53DwVRMYO3t5Yr&index=3
can somebody explain pls

[signal tapir]

1. Ask your question and show the work you've done so far. If you've posted a screenshot of a question, specify which part you need help with.
2. Wait patiently for a helper to come along.
3. Once someone helps you, say thank you and close the thread with:

   +close
   

4. Feel free to nominate the person for helper of the week in #helper-nominations
5. Do not ping the mods, unless someone is breaking the rules.
6. If you're happy with the help you got here, and the server overall, you can contribute financially as well:

[hollow grotto]

pls help

[hidden garden]

https://youtu.be/o1zYYT0fDkA?si=gzObvgjxXRX7QnPS

[proper radish]

OP needed help with one video and Brodie sent another video

[hidden garden]

Yeah sorry, I'm not good at explaining. And I never questioned why cos x is -sin x since all you have to do in derivatives is memorize the table.

[hollow grotto]

I was thinking to do it graphically

not with this

[hollow grotto]

[worthy onyx]

What have you tried?

Show us what you did and we might help you with finding and correcting your line of thinking

[summer pagoda]

Geometric reasoning has limits. In particular, in geometry, lengths must always be nonnegative.

Especially when you're considering right triangle trigonometry. All trigonometric values in that context are nonnegative because the angle can only range from 0 to pi/2.

[honest lynx]

The direction of dθ is up and to the left, meaning that sin(θ) is going up but cos(θ) is going down. That is, d(cos(θ)) is negative.

meaning d(cos(θ)) is -1 * <side length>, not <side length>

[hollow grotto]

how does it go down?

and why?

[lilac mango]

Positive x-axis points towards the right, doesn't it?

[hollow grotto]

wait

I will show what I did

correct me pls

i am getting wierd values

[hollow grotto]

here

[hollow grotto]

pls check it out

[lilac mango]

The length isn't d(cos(theta)), it is |d(cos(theta))|

[hollow grotto]

but still it will be sin of theta not - sin theta

right?