the asymptotic notation big o is considered as upper bound or worst case so the graph of f(n) is never goes across the c.g(n).
c.g(n) > f(n)
f(n ) <= c.g(n)
so we can conclude that
we can understand this by if we consider that we have to fine one element in the array then we follow the linear search algorithm and find that elements so the worst case will be the element is not present in the array or it will be the last element.
so i hope you will understand in my next article we will solve some problem on it.