You are Here: Home >< Maths

# Differential of cos(piy) watch

1. How do I differentiate cos(piy)?

Should I use chain rule??
2. The differential of any cos(f(x)) is -f'(x)sin(f(x))

Eg d(cos(2x))/dx = -2sin(2x)
3. (Original post by Cerdic)
The differential of any cos(f(x)) is -f'(x)sin(f(x))

Eg d(cos(2x))/dx = -2sin(2x)
So it's just -pisin(y)?

No dy/dx or anything?
4. (Original post by Dinasaurus)
So it's just -picos(y)?

No dy/dx or anything?
You haven't said what you're differentiating with respect to, but assuming it's y, then the answer would be
5. (Original post by Dinasaurus)
So it's just -pisin(y)?

No dy/dx or anything?
.
6. (Original post by B_9710)
.
Or that if you're differentiating wrt x
7. (Original post by B_9710)
.
Where does that dy/dx come from? What method would be used to do this or is this just something I am expected to know?
8. (Original post by Dinasaurus)
Where does that dy/dx come from? What method would be used to do this or is this just something I am expected to know?
Well
See how the dy on the top and bottom kind of cancel out leaving just d/dx (cosπy). That's what you do. Differentiate the function with respect to y then multiply by dy/dx.

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 13, 2016
Today on TSR

### 2,195

students online now

Exam discussions

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams