Find the Derivative $$r = 20 - \theta ^ { 4 } \cos \theta$$

Multiple Choice

Find the derivative.
- $$r = 20 - \theta ^ { 4 } \cos \theta$$

A) $\frac { \mathrm { dr } } { \mathrm { d } \theta } = 4 \theta ^ { 3 } \sin \theta - \theta ^ { 4 } \cos \theta$
B) $\frac { \mathrm { dr } } { \mathrm { d } \theta } = 4 \theta ^ { 3 } \sin \theta$
C) $\frac { \mathrm { dr } } { \mathrm { d } \theta } = 4 \theta ^ { 3 } \cos \theta - \theta ^ { 4 } \sin \theta$
D) $\frac { \mathrm { dr } } { \mathrm { d } \theta } = - 4 \theta ^ { 3 } \cos \theta + \theta ^ { 4 } \sin \theta$