x Turn on thread page Beta
 You are Here: Home >< Maths

# C4 Differentation watch

1. I have been doing some C4 practice papers and there is the one question that I cannot get the right answer for.

Find the value of f'(x) at the value x=Pi/3 for f(x)=tan2xsinx

Now, I can get so far as getting f'(x) and according to the answer booklet it is correct at f'(x)=2.sec^2.2x.sinx + tan2x.cosx but when I substitute in Pi/3 I keep coming up with a wrong answer.

Please could someone help. Thank you
2. f'(x)=2.sec^2.2x.sinx + tan2x.cosx when x=pi/3
= 2 x 4 x 0.866 + -1.732 x 0.5
=6.928 - 0.866
=6.06 (3sf)

Is this either of the answers you have?
3. r u sure u set ur calculator on "radians"?
4. (Original post by franks)
f'(x)=2.sec^2.2x.sinx + tan2x.cosx when x=pi/3
= 2 x 4 x 0.866 + -1.732 x 0.5
=6.928 - 0.866
=6.06 (3sf)

Is this either of the answers you have?
Seems to be correct
5. Yes that is what I have been getting but the answers at the back say that it is wrong. Nevermind, I will put it as that. Thank you.
6. (Original post by BS-E-M-Student)
Yes that is what I have been getting but the answers at the back say that it is wrong. Nevermind, I will put it as that. Thank you.

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: April 14, 2006
Today on TSR

### How much will your degree earn you?

Find out where yours ranks...

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