I need help on math please..

there are 6 terms on varaible expression

F(x) = 5cos(1/2x) - 2
g(x) = 5cos(x) - 2

The period for a cosine function is 2pi/k
In the equation the k is  located before the variable.
In g(x) we have 5cos (1x) -2
so the period is 2pi/1 or 2pi. This means the length of one full period of cosine will go from 0 to 2pi.

In f(x) we have 5 cos (1/2 x) - 2
so the period is 2pi/ (1/2) which is the same as 2pi * 2 or 4pi.
This means the period for the function is 4pi and the length of one full period of the cosine graph will go from 0 to 4pi.
The length of f(x) will be longer than that of g(x) .