Wave optics

ANS D


@HarshalSolanki
Why here we are not applying this formula.

@YouKnowwhere which formula is this ?
What is nb on lhs there?

@HarshalSolanki n th bright fringe measeured from mean line.

@YouKnowwhere
I hv never seen that formula i think it shud be like this bcoz in lhs u said it is y of nth fringe and also the first term of rhs is y of nth fringe