# What is the period of f(t)=cos 9 t ?

Period $= \frac{2 \pi}{\left\mid 9 \right\mid} = \frac{2 \pi}{9}$

#### Explanation:

from the equation $y = a \cos b x$

the formula for period $= \frac{2 \pi}{\left\mid b \right\mid}$

from the given $f \left(t\right) = \cos 9 t$

$a = 1$ and $b = 9$

period $= \frac{2 \pi}{\left\mid 9 \right\mid} = \frac{2 \pi}{9}$

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