# What is the frequency of f(theta)= sin 7 t - cos 9 t ?

${\left(4 \pi\right)}^{2} / 63$
Frequency of sin 7t --> $2 \frac{\pi}{7}$ or 360/7 deg
Frequency of cos 9t --> $\frac{2 \pi}{9}$ or 360/9 deg
Frequency of (ft) --> $\left(\frac{2 \pi}{7}\right) \left(\frac{2 \pi}{9}\right) = {\left(4 \pi\right)}^{2} / 63$
or $\left(\frac{360}{7}\right) \left(\frac{360}{9}\right) = \left(\frac{129 , 600}{63}\right)$ deg