Question

What is the Period of the function y=cos (x/5)?
I know that the formula for period is 2pi/Absolute value of b.

Answer 1

here's a way to remember this if you like

the normal formulation [in physics\engineering] is \(y = \cos \omega x\).

\(\omega\) is the angular speed [or angular frequency] measured in radians per second

using a simple distance-speed-time formula for angular motion, you can say that \(\omega = \dfrac{2 \pi}{T}\) where T is the period

[for completeness, you can also say that \(\omega = 2 \pi f\) where fi is the ordinary frequency measured in Hertz ie oscillations per second]

so here you have \(\omega = \dfrac{1}{5}\) and you can now do the rest.....

Answer 2

so 2pi/1.5 !?

Answer 3

from \(\omega = \dfrac{2 \pi}{T}\) you can say \(T = \dfrac{2 \pi}{\omega} = \dfrac{2 \pi}{\frac{1}{5}} = \dots\)