different answers for derivative?(Solved)

Take this trigonometric function:

Using the chain rule i think it becomes:

But if we use the identity:

then the equation becomes

But if,

then,

Which doesn't appear so. Why am I getting different answers for the same derivative? Did I do something wrong in the above steps?

I accidentally took :

(Headbang)

P.S. This is my first post and using [tex] is VERY slow and irritating, is there a faster way to insert math expressions :confused:

Re: different answers for derivative?

Quote:

Originally Posted by

**dhtikna** Take this trigonometric function:

Using the chain rule i think it becomes:

This part of the post is correct. But none of the rest makes any sense.

It is the case that . But that cannot be simplified.

They both have the same derivative.

Re: different answers for derivative?

but you have which is NOT .

Re: different answers for derivative?

I Can't belive i was so stupid. I hadn't been doing trig for a long time so i messed up when I took:

By the way, any have a answer to my P.S.:

P.S. This is my first post and using [tex] is VERY slow and irritating, is there a faster way to insert math expressions

Re: different answers for derivative?

Quote:

Originally Posted by

**dhtikna** I Can't belive i was so stupid. I hadn't been doing trig for a long time so i messed up when I took:

By the way, any have a answer to my P.S.:

P.S. This is my first post and using [tex] is VERY slow and irritating, is there a faster way to insert math expressions

Yes, get good at copying and pasting the preamble, learn the code and type faster :P