Find the minimum value of x for which a maxima is obtained at P.

Explanation

For maxima, `Delta x = lambda` (because x should be minimum) Path difference between the direct & reflected ray
`= x +(lambda)/(2)+x`
(due to reflection, a phase change of `pi` or path change of `(lambda)/(2)` takes place)
`therefore lambda = x +(lambda)/(2)+x`
`2x=(lambda)/(2)`
`rArr x = (lambda)/(4)`