Derivative of (4995)/(1+.12cosθ) with θ = 120° - Simple Calculus Problem

[LyleCoff]

Find the derivative of (4995)/(1+.12cosθ), when θ = 120°

My attempt:

d/dx [4995/(1+.12cosθ) = (4995)(-1)(1+.12cosθ)^-2(.12)(-sinθ)

Letting θ = 120°...

= (4995)(-1)(1+.12(-1/2))^-2(.12)(-\sqrt{3}/2)

My calculator says that is about 587.478

But it's supposed to be about 10.253

I just started calculus, so I'm probably making some really basic mistake.

 

[Bacle2]

Results are usually done in radians instead of degrees. Have you tried doing your

computation in radians?

 

[LCKurtz]

To add to what Bacle2 has said, your standard formulas for the derivatives are correct only when the angles are given in radians.