# What is the period of f(t)=sin( ( 7 t ) /5 ) ?

$\left(\frac{10}{7}\right) \pi$
$\sin k \left(t + \frac{2 \pi}{k}\right) = \sin \left(k t + 2 \pi\right) = \sin k t$
So, the period of sin kt is $\frac{2 \pi}{k}$.
Here, k = $\frac{7}{5}$. So, the period is $\frac{10 \pi}{7}$..