# derivaties of Trigonometric Functions

• Aug 25th 2007, 11:56 AM
keith
derivaties of Trigonometric Functions
Here is another one I am stuck on.
5sinx/(1+cosx)
this is what I did:

(1+cosx)d/dx[5sinx]-(5sinx)d/dx[1+cosx]/(1+cosx)^2

([1+cos(x)]*(-5)*cos(x)-[5+sin(x)]*[-sin(x)])/([1+cos(x)]^2)

Where did I go wrong here?

Thank you!
Keith
• Aug 25th 2007, 12:00 PM
Krizalid
Quote:

Originally Posted by keith
5sinx/(1+cosx)

$f(x)=\frac{5\sin x}{1+\cos x}=5\sin x\cdot(1+\cos x)^{-1}$

Use the product rule.
• Aug 25th 2007, 12:48 PM
keith
Quote:

Originally Posted by Krizalid
$f(x)=\frac{5\sin x}{1+\cos x}=5\sin x\cdot(1+\cos x)^{-1}$

Use the product rule.

I looked over the problem and noticed it should have been:
(1+cosx)(5cosx) not -(5cosx)
Thanx anyway
• Aug 25th 2007, 12:51 PM
Krizalid
Quote:

Originally Posted by keith
(1+cosx)(5cosx)

If you wanna derive this, then just expand $5\cos x+5\cos^2x$

Then apply simple rules of derivation.