whats the period, amplitude and midline equation of y=1\4 cos 2pi\3

I'll assume that you actually mean

 

$$\\y=(1/4 )\;cos [(2\pi/3)x]\\\\
Period=2\pi \div \frac{2\pi}{3}=2\pi\times\frac{3}{2\pi}=3\\\\
Amplitude=1/4\\\\
middle : \qquad y=0\;\;\;$(the x axis)$$$

 

Here isa the graph

 

https://www.desmos.com/calculator/jqfuaxzoua