# Can we apply binary search for finding key 'x' in unsorted array?

Suppose we are given A, an array of size n, comprised of an increasing sequence of numbers followed immediately by a decreasing one. What is worst case time complexity of optimal algorithm to determine if a given number x is in the array?

The explanation given on the this site is confusing to me. How we can apply binary search on unsorted array?

They have provided following explanation => This is an application of Binary search, which has time complexity $Θ(log n)$ in worst case.